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__GFP_NOFAIL should not be used in new code [1]. xive_init_ipis()
allocates the xive_ipis array with __GFP_NOFAIL, which makes the
subsequent NULL check unreachable dead code.
Remove __GFP_NOFAIL so the allocation can fail, and make all xive_ipis
access paths NULL-safe:
- Return XIVE_BAD_IRQ from xive_ipi_cpu_to_irq() when xive_ipis is NULL.
- Set xive_ipis to NULL after kfree() in the error path to prevent
use-after-free.
- Guard xive_setup_cpu_ipi() and xive_cleanup_cpu_ipi() against
xive_ipi_irq == XIVE_BAD_IRQ to avoid dereferencing an uninitialized
or already-freed xive_ipis array.
No functional change when allocation succeeds.
Link: https://lore.kernel.org/all/20260725202632.dcb325658896a470df91cf57@linux-foundation.org/ [1]
Fixes: 7dcc37b3eff9 ("powerpc/xive: Map one IPI interrupt per node")
Signed-off-by: Gou Hao <gouhao@uniontech.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Cédric Le Goater <clg@kaod.org>
Suggested-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Reviewed-by: Wentao Guan <guanwentao@uniontech.com>
Reviewed-by: jiazhenyuan <jiazhenyuan@uniontech.com>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260727104215.184786-2-gouhao@uniontech.com
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All other fields have comments describing them, add one for this field
as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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Allocating the new bio for a split from the same pool as the original
one can deadlock under memory pressure as the origin bio could be the
last one from the mempool.
Add a separate pool for splitting GC write bios to avoid this.
Fixes: 080d01c41d44 ("xfs: implement zoned garbage collection")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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xlog_recover_dquot_commit_pass2() validates the recovered dquot with
xfs_dqblk_verify() and, on failure, sets error = -EFSCORRUPTED and jumps
to out_release. But out_release unconditionally returns 0, so the
corruption error is discarded: the caller xlog_recover_items_pass2()
sees success, log recovery proceeds as if the dquot were valid, and the
corrupt quota buffer can be written back to disk.
Fixes: 9c235dfc3d3f ("xfs: dquot recovery does not validate the recovered dquot")
Cc: stable@vger.kernel.org # v6.8
Signed-off-by: Long Li <leo.lilong@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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xfs_dq_get_next_id() takes the quota inode ILOCK before calling
xfs_iread_extents(). If xfs_iread_extents() fails, the function returns
immediately without releasing the lock, leaking the quota inode ILOCK.
This can leave the quota inode locked and cause subsequent quota
operations to hang.
Fix this by jumping to a common unlock path on error instead of returning
directly.
Fixes: bda250dbaf39f ("xfs: rewrite xfs_dq_get_next_id using xfs_iext_lookup_extent")
Cc: stable@vger.kernel.org # v4.12
Signed-off-by: Long Li <leo.lilong@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM complained that this function ignores runtime errors being
returned by xrep_iunlink_store_*. Rework the function signature so that
we can return runtime errors to abort the repair.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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If we find a rogue free inode and decide to reinsert it into the
unlinked list, we need to set the prev pointer to NULLAGINO so that the
incore list gets updated.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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xrep_iunlink_resolve_bucket is supposed to reconstruct as much of the
incore prev and next unlinked list pointers based on what it finds on
disk and in memory before we move on to relinking the truly lost inodes
back into the unlinked list. However, it's still vulnerable to infinite
loops that come in via the next_unlinked pointers.
Fix this problem by remembering which inodes we've already seen and
checking new agino pointers against that. If a bit is already set,
either this is a loop or the inode has nonzero link count. We'll deal
with the second case in a subsequent patch.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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If an allocated inode shows up in the unlinked list, we need to get it
completely off the list. Set the corrected next/prev pointers such that
the inode will not look like it should be on an unlinked list at all.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM noticed that we neglect to check for xfarray_iter itself returning
errors when writing a new AGI. Fix that.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM points out that the only error that xrep_iunlink_mark_ondisk_rec
returns is ENOMEM, but we ignore that, and can end up writing a garbage
AGI based on incomplete information. We shouldn't do that, though here
we must be screen out EFSCORRUPTED/EFSBASDCRC because we haven't
checked the inobt yet.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM notices that xrep_iunlink_relink_prev has the comment "set the
forward pointer..." but then loads the value from the xfarray that
stores pointers to the previous inode in the unlinked list. That's
wrong, so fix the variable access.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM noticed a longstanding bug where xrep_iunlink_walk_ondisk_bucket
tries to walk ragi->sc->sa.agi_bp to rebuild the unlinked inode lists.
Unfortunately, it's possible for agi_bp to be null if the buffer
verifier fails, so we have to use ragi->agi_bp (which skips verifier
checks) instead.
Cc: stable@vger.kernel.org # v6.10
Fixes: ab97f4b1c03075 ("xfs: repair AGI unlinked inode bucket lists")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM points out that online fsck can livelock if an unlinked inode list
contains a loop. Use a bitmap to detect cycles.
Cc: stable@vger.kernel.org # v4.15
Fixes: a12890aebb8959 ("xfs: scrub the AGI")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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In the next patch we're going to make this loop more exciting, so hoist
the code to a helper function to reduce clutter in the resulting code.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM noticed a potential UAF if the tempfile creation code fails after
it set sc->tempip. Fix that.
Cc: stable@vger.kernel.org # v6.10
Fixes: 84c14ee39dd388 ("xfs: create temporary files and directories for online repair")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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In xchk_nlinks_ilock_dir, take the IOLOCK before accessing internal
inode state to figure out if we need to take ILOCK shared or exclusive.
That way we can't race with directory updates. LOLLM pointed out that
the code was initially correct w.r.t. the IOLOCK, but then I broke it.
Cc: stable@vger.kernel.org # v6.18
Fixes: f477af0cfa0487 ("xfs: fix locking in xchk_nlinks_collect_dir")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM noticed that xrep_xattr_rebuild_tree doesn't check for queued
parent pointer updates when it decides that it's going to zap the attr
fork. This is obviously incorrect, so fix that. We hold the IOLOCK and
the ILOCK of sc->ip at that point in time, so we can't race with any
/new/ operations.
Cc: stable@vger.kernel.org # v6.10
Fixes: e5d7ce0364d8ee ("xfs: replay unlocked parent pointer updates that accrue during xattr repair")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM noticed that scrub sets the CORRUPT flag when xfs_parent_from_attr
thinks it's been given a corrupt parent pointer. This eliminates the
potential to repair the filesystem because that error code is bubbled up
the call stack. Fix this by collapsing them all to ECANCELED in
xchk_parent_pptr, which doesn't have that trait.
Cc: stable@vger.kernel.org # v6.10
Fixes: 0d29a20fbdba89 ("xfs: scrub parent pointers")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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LOLLM notices that the dirtree scrubber can detect a directory that
refers to itself. In this case, it's not correct for the directory tree
repair code to try to iolock/ilock both sc->ip and dp, because they're
the same inode. Fix this by detecting that corner case and handling it
appropriately.
Cc: stable@vger.kernel.org # v6.10
Fixes: 3f31406aef493b ("xfs: fix corruptions in the directory tree")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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In the cntbt (free space by block count) btree, records are not supposed
to be in startblock order. Hence the mergeability check is pointless.
Remove it, since it does nothing, as LOLLM points out.
Cc: stable@vger.kernel.org # v6.4
Fixes: d5784ae82778d9 ("xfs: flag free space btree records that could be merged")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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sashiko.dev noticed that these checks clear all the valid flags instead
of invalid. This probably was never hit as it only executed on invalid
flag presence.
Fixes: 2d295fe65776 ("xfs: repair inode records")
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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When exchanging two full-file ranges, xmi_can_exchange_reflink_flags()
can move the reflink inode flag from the file that currently has it to
the other file, as long as exactly one side is marked. This assumes
that the file contents, and therefore all shared extents, are exchanged.
That assumption is not true when XFS_EXCHMAPS_INO1_WRITTEN is set.
xfs_exchmaps_can_skip_mapping() can skip hole and unwritten mappings
from file1, so an exchange can complete without moving every mapping
that the earlier flag-swap decision accounted for. In that case the
post-operation cleanup can clear the reflink flag from an inode that
still owns shared written extents. Later writes then take the
non-reflink write path and may update blocks that should still have
been protected by CoW, which shows up as data corruption between
reflink-related files.
Fix this by disabling the reflink flag exchange whenever
XFS_EXCHMAPS_INO1_WRITTEN is requested. The contents exchange can still
proceed; the conservative outcome is that both inodes keep the reflink
flag. The regular reflink flag cleanup path can drop the extra flag
later once the inode no longer has shared extents.
Reported-by: Lin Jiapeng (TencentOS Red Team) <jiapenglin@tencent.com>
Fixes: 966ceafc7a43 ("xfs: create deferred log items for file mapping exchanges")
Cc: stable@vger.kernel.org # v6.10
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lin Jiapeng <jiapenglin@tencent.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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uretprobes_srcu currently uses normal SRCU, which issues
two smp_mb() per read lock/unlock pair. This overhead is
paid on every uretprobe hit.
Switch to SRCU-fast-updown, which eliminates the per-reader
memory barriers by moving the ordering cost to the
grace-period side (synchronize_rcu() instead of smp_mb()).
This is acceptable because grace periods (uprobe
unregistration) are infrequent compared to reader-side
uretprobe hits.
The updown flavor is required because the SRCU read lock is
taken in prepare_uretprobe() when a return instance is
created and is held until that return instance is finalized.
The traced thread returns to user space in between, so the
lock is inherently released in a different context from
where it was acquired: on the normal return path via
uprobe_handle_trampoline() -> hprobe_finalize(), or from
ri_timer() (expiry) or dup_utask() (fork) via
hprobe_expire(). srcu_down_read_fast() / srcu_up_read_fast()
are designed for this acquire-here / release-elsewhere
pattern and, unlike the same-context srcu_read_lock_fast()
variant, do not carry the lockdep read-side tracking that
would warn on it.
The short, same-context SRCU sections in ri_timer() and
dup_utask() (which guard the uprobe against reuse across the
hprobe_expire() cmpxchg) instead use guard(srcu_fast_updown)
for proper lockdep coverage.
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://patch.msgid.link/20260706172744.3920417-3-puranjay@kernel.org
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Add a guard(srcu_fast_updown) definition for scoped
SRCU-fast-updown read-side critical sections, following the
existing pattern of guard(srcu) and guard(srcu_fast).
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://patch.msgid.link/20260706172744.3920417-2-puranjay@kernel.org
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An 'F' entry whose interpreter keeps the binfmt_misc superblock alive
pins the instance that owns it forever. Cover both ways to build that:
- an interpreter on the instance's own files, control file and entry
file alike
- and an instance used as an overlayfs lower layer.
Check that an ordinary 'F' registration still succeeds so the fix stays
honest about not changing what 'F' promises.
Link: https://patch.msgid.link/20260728-work-binfmt_misc-selfpin-v1-2-74df5daeca5b@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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An entry is matchable as soon as it is registered. create_entry() sets
the enabled bit for every type and add_entry() links it straight into the
instance, so everything an entry needs has to fit in the write that
creates it.
Add a 'D' flag. The entry is created disabled and has to be enabled by
writing '1' to its entry file before it can match anything. That splits a
registration into create and activate, which a later patch uses to
configure an entry beyond what one register string can carry. It is
useful on its own too. Entries can be staged without dispatching the
moment they are written.
A staged entry stays out of the search list entirely. add_entry() only
hashes an entry that is born matchable, and the first '1' written to
the entry file hashes a staged one, which takes its place in the search
order at that point. The rcu insertion publishes the fully configured
entry, so the exec side keeps the plain enabled test it always had.
Removal cannot rely on the search list anymore. Whether an entry was
already removed is now decided by its dentry, '-1' to the status file
walks the directory instead of the list so staged entries do not
survive it, and a '1' through a file handle held across a removal
publishes nothing.
'D' is consumed at registration and not recorded. What matters afterwards
is whether the entry is enabled, and the entry file already reports that.
A 'B' entry's flags field had to be empty so far because every flag it
could name shaped the invocation, which a bpf handler picks per exec with
bpf_binprm_set_flags(). 'D' shapes the registration instead. So the rule
becomes what it always meant: a 'B' entry carries no invocation flags,
and 'D' composes.
Link: https://patch.msgid.link/20260730-work-binfmt_misc-preopen-v1-1-4a0b0da71f16@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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loader substitution"
Christian Brauner <brauner@kernel.org> says:
binfmt_misc has exactly one execution model where the registered
interpreter becomes the executed program and the matched binary is
handed to it as an argument. For wine or qemu-user that is the point.
For a per-binary loader it is backwards. The interpreter is an
implementation detail of running the binary, yet it owns the entire
process identity:
- argv[0] and /proc/pid/cmdline show the interpreter invocation, not
what the caller executed.
- /proc/self/exe names the interpreter. Relocatable programs commonly
locate themselves through it and find the dynamic linker instead.
- A binary passed to execveat() as an inaccessible O_CLOEXEC fd
cannot run at all as the interpreter has no path to open it by.
- gdb cross-validates AT_ENTRY/AT_PHDR against the exe file and
discards the load displacement on mismatch leaving PIE symbols
unrelocated.
This series adds two dispatch modes that close the gap from opposite
ends:
(1) transparent dispatch
Registered with the 'T' flag or chosen per exec with
BPF_BINPRM_TRANSPARENT. The binary is sent to the interpreter through
AT_EXECFD, the argument vector stays exactly as the caller built it,
and the kernel labels mm->exe_file and comm with the binary. A new
AT_FLAGS_TRANSPARENT_INTERP aux vector bit is raised indicating that
nothing was spliced, argv belongs to the program, and to load it from
the descriptor.
The interpreter keeps control of mapping the binary, so the mode
covers foreign architectures and non-ELF payloads.
The exe label is not a new privilege. It names precisely the file the
caller passed to execve(), not a file of the process's choosing. That
file is permission-checked, write-denied while the process runs and
recorded by audit. Credential derivation does not change exactly as
today.
(2) loader substitution
The kernel executes the matched binary natively as the main image
and substitutes the registered interpreter for the binary's
PT_INTERP. binfmt_misc functions as a PT_INTERP override. There is
no contract and no identity to reconstruct. So a stock dynamic
loader works unchanged. Hence, 'L' is for native-arch ELF with
PT_INTERP.
The two modes compose. A bpf handler reads the ELF header from bprm->buf
and grades per binary, picking 'L' where it applies and 'T' or classic
dispatch for the rest. If userspace control over relocation is wanted
'T' is the way to go.
* patches from https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-0-e57866e4ae0f@kernel.org: (21 commits)
binfmt_misc: document loader substitution
selftests/exec: test binfmt_misc loader substitution
binfmt_misc: let a bpf handler request loader substitution
binfmt_misc: add the 'L' loader substitution flag
binfmt_elf_fdpic: consume a stashed PT_INTERP substitute
binfmt_elf: consume a stashed PT_INTERP substitute
exec: carry a PT_INTERP substitute in struct linux_binprm
binfmt_misc: document the transparent identity contract
selftests/exec: test the transparent binfmt_misc mode
binfmt_misc: let a bpf handler run the interpreter transparently
binfmt_misc: add a static transparent flag 'T'
binfmt_misc: add transparent interpreter dispatch
exec: label mm->exe_file with the binary for a transparent dispatch
exec: add AT_FLAGS_TRANSPARENT_INTERP
selftests/exec: convert the binfmt_misc bpf test to the kselftest harness
exec: release the replaced file with do_close_execat()
binfmt_misc: split out entry_open_interpreter() and build_interp_argv()
binfmt_misc: normalize the per-exec invocation flags
binfmt_misc: table-drive the register string flags
docs, binfmt_misc: keep general usage out of the handler sections
...
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-0-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Describe the L mode next to the transparent one.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-21-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Exercise the 'L' flag end to end. The payload runs as the main image
with a copy of the system loader substituted for its PT_INTERP, and
asserts the native identity from inside:
- argv exactly as the caller built it
- no AT_EXECFD
- AT_FLAGS clear
- AT_BASE set but outside its own image
- AT_PHDR/AT_ENTRY inside it
- /proc/self/{exe,comm,stat} and AT_EXECFN all describing the binary
- ETXTBSY on the running binary
- the substituted loader visible in /proc/self/maps under its real path
Magic matching pokes a marker into the ELF header's e_ident padding
(EI_PAD, offset 9), which sits inside the match window and is ignored by
kernel and loader alike. the same binary is also matched by extension.
Two cases cover the paths where the substitution does not happen. A '#!'
file that matched an 'L' entry is claimed by binfmt_script rather than by
binfmt_elf, so the staged substitute has to be released when the
interpreter replaces the file; the test opens the loader for writing
afterwards, which fails with ETXTBSY if the write denial was leaked
instead. A relative interpreter path is rejected at registration for both
'L' and 'C', neither of which may resolve one against the working
directory of whoever runs the binary.
The bpf-side BPF_BINPRM_LOADER path shares all machinery past the flag
mapping. A harness case for it can join the bpf runtime coverage of
the transparent series.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-20-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Give bpf handlers the per-exec equivalent of the static 'L' flag. A
load program that sets BPF_BINPRM_LOADER has its selected interpreter
substituted for the binary's PT_INTERP instead of run with the binary
as payload. The binary otherwise executes as a fully native exec.
A single handler can now grade its dispatch per binary: native-arch ELF
with PT_INTERP gets loader substitution for full native identity.
Anything else, such as foreign arch, static, non-ELF can use transparent
or classic dispatch. The load program can read the binary's ELF header
from bprm->buf to make that call.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-19-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Add the first activation of the PT_INTERP substitution machinery. A
static entry registered with the new 'L' flag no longer runs the
registered interpreter with the binary as payload. It stashes the
interpreter as bprm->loader and declines the match with -ENOEXEC. The
format search continues in the same round. binfmt_elf claims the binary
as a fully native exec and substitutes the stashed file for the binary's
PT_INTERP.
'L' rejects every classic-dispatch flag at registration. 'T', 'P' and
'O' have nothing to act on (no argv splice, no execfd) and 'C' is
subsumed (credentials derive from the binary natively). 'F' composes and
is valuable: with it the substitute is pre-opened at registration time
and immune to mount namespace changes. Without it the substitute is
opened at exec time in the exec'ing task's context, so 'L' joins 'C' in
the requirement that the interpreter be named by an absolute path. As
with 'C', only trusted interpreters should be registered. The
substituted loader runs with credentials derived from the binary.
Like the other flag characters 'L' cannot be used as the field
delimiter. The flag scan would run off the registration buffer.
The interpreter open is shared with the classic path via the
entry_open_interpreter() helper. An open error fails the exec. Map
-ENOEXEC to -EACCES to avoid letting the binary run with its own
PT_INTERP.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-18-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Do what binfmt_elf does. When a binfmt_misc loader entry stashed
bprm->loader use it in place of the path named in PT_INTERP, and drop the
override when the binary names no interpreter at all.
Without this 'L' is unusable on nommu, where fdpic is the only ELF
loader. On ARM with an MMU both loaders are registered but split the ELF
space between them along elf_check_fdpic(), so an fdpic binary is never
picked up by binfmt_elf either.
Declining is what fdpic did so far, but it declined late. The pending
override was only caught in begin_new_exec(), by which point the segment
scan had opened the interpreter the binary itself names and overwritten
bprm->buf with its header, leaving the next format in the round to
inspect a buffer that no longer describes the file it is offered. The
scan consumes the override now, so of the in-tree formats only
binfmt_flat still relies on the refusal, and it reads bprm->buf without
writing it.
Transparent dispatch needs nothing on top of the AT_FLAGS translation
both loaders already share. The binary travels in AT_EXECFD, which
create_elf_fdpic_tables() emits, and the exe and comm labelling is done
in exec.c for every format.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-17-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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When a binfmt_misc loader entry stashed bprm->loader use it instead of
opening the path named in PT_INTERP. The substitution deliberately
changes as little as possible. Ownership transfers into the local
interpreter reference which the existing success and error paths already
release.
A binary without PT_INTERP has nothing to substitute for. Drop the
override at the end of the segment scan and load the binary natively.
Nothing sets bprm->loader yet.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-16-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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binfmt_misc currently supports an execution model where the registered
interpreter becomes the executed program and the matched binary is
handed to it as payload. The upcoming binfmt_misc loader mode inverts
this. The matched binary remains the executed program and the registered
interpreter is substituted into the role the binary's PT_INTERP would
have played.
Add the channel for that hand-over. bprm->loader carries an
open_exec-style struct file reference from the binfmt_misc match to the
binary format that consumes it. Unlike bprm->interpreter it does not
request a restart of the format search. The stashing handler declines
the exec with -ENOEXEC and the search continues to the real format in
the same round.
Both ELF loaders consume it, so give them the two helpers to do it with
rather than a copy each. bprm_open_interpreter() hands out the substitute
in place of what PT_INTERP names and bprm_drop_loader() releases one that
turned out not to apply.
Establish the complete lifecycle up front so a stashed loader can
neither leak nor be silently ignored.
- Chain restart: if another format wins the round by staging
bprm->interpreter (binfmt_script) the stashed loader belonged to
the file being replaced. Drop it at the top of the swap block in
exec_binprm().
- Unclaimed or error: free_bprm() releases a still-stashed loader
next to the other bprm file references.
- Silent non-substitution: a final format that reaches
begin_new_exec() with a pending loader would run the binary while
ignoring the override. Refuse with -ENOEXEC before the point of no
return. Formats that do not know about the override (binfmt_flat,
out-of-tree) need no changes.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-15-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Describe what a transparent dispatch constructs and the loader contract
behind AT_FLAGS_TRANSPARENT_INTERP. Also note what deliberately stays
different (the address space layout) and what stays unchanged
(credential derivation without 'C').
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-14-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Verify the identity a transparent dispatch constructs, from both
activation paths.
- binfmt_misc_transparent: registers a magic entry with the static 'T'
flag and execs a matched binary with arguments.
- binfmt_misc_bpf: a handler whose load program sets
BPF_BINPRM_TRANSPARENT.
Both dispatch to a shared asserting interpreter that runs in place of
the binary and checks the contract from the inside:
- AT_FLAGS carries AT_FLAGS_TRANSPARENT_INTERP
- AT_EXECFD refers to the very inode of the binary
- /proc/self/exe resolves to the binary
- argv and /proc/self/cmdline are exactly what the caller passed with
nothing spliced in
- comm is the binary's basename
- the binary is write-denied while it runs
The static test also validates the registration. 'T' combined with 'P'
must be rejected. A kernel that does not know 'T' turns the test into a
skip. The asserting interpreter and the static test build without the
bpf toolchain so the core transparent semantics stay covered on systems
where the bpf cases are skipped.
The flag support probe, the canonical payload argv with the
run_payload() helper that execs it, and the identity assertions (exe
link, comm, write denial) live in binfmt_misc_common.h; the loader
substitution test reuses all of them.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-13-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Expose transparent mode 'T' to the bpf handler via a new
BPF_BINPRM_TRANSPARENT flag. A bpf handler can decide per binary whether
the dispatch is transparent. This way users may choose a native-looking
loader for one binary and a visible wrapper invocation for the next.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-12-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Let a registration opt into transparent dispatch. The 'T' flag lets a
matched binary keep its argument vector and is sent to the interpreter
through AT_EXECFD. The process's identity is the binary's.
'T' implies 'O' exactly like 'C' does. 'P' is rejected in combination
with it. Transparency preserves the whole argument vector so there is
nothing left for 'P' to say. 'C' remains an independent choice and 'F'
keeps working. A pre-opened interpreter is orthogonal to how the binary
is handed over.
Like the other flag characters 'T' cannot be used as the field
delimiter. The flag scan would run off the registration buffer.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-11-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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A binfmt_misc interpreter is visible to the binary it runs. argv[0]
becomes the interpreter path and the binary's path is appended as an
argument and /proc/pid/cmdline shows both. For wine or qemu-user that is
the point. For a per-binary loader the interpreter is an implementation
detail of running the binary that has no business in the argument
vector. And a binary handed to execveat() as an O_CLOEXEC fd without a
usable path cannot be run through binfmt_misc at all. The interpreter
would have no path to open the binary by.
Add the dispatch machinery for a transparent mode. The binary is handed
to the interpreter through AT_EXECFD. The argument vector is left
exactly as the caller set it. argv[0] and /proc/pid/cmdline look like a
direct execution of the binary. bprm->interp still names the
interpreter: it drives the next format lookup and the
sched_prepare_exec tracepoint, not what the process sees.
The interpreter loads the binary from AT_EXECFD for this. A relocatable
loader can and glibc's ld.so is gaining AT_EXECFD support [1]. A staged
interpreter argument is rejected: no argv slot is built for it to land
in.
The transparent branch raises BINPRM_FLAGS_TRANSPARENT_INTERP. A
dispatch through it labels mm->exe_file with the binary and raises
AT_FLAGS_TRANSPARENT_INTERP next to AT_EXECFD. The aux vector bit is the
loader's hint to retarget saved_auxv and the statistics markers to the
binary, which is only correct while the exe link names the binary too.
The inaccessible-path bail moves after handler selection and into the
path-building branch. A transparent interpreter takes the binary from
AT_EXECFD instead of a path, so the restriction does not apply to it
and the O_CLOEXEC execveat() case above can work. Nothing can take the
transparent branch yet.
Link: https://inbox.sourceware.org/libc-alpha/20260717-work-glibc-binfmt_misc-v3-0-45129bfb13fe@kernel.org [1]
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-10-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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When binfmt_misc dispatches a binary to an interpreter, the interpreter
becomes bprm->file and begin_new_exec() labels mm->exe_file with it. For
wine or qemu-user that is the point. For the transparent mode it
defeats the point. The interpreter is an implementation detail and the
process's identity is the binary. Relocatable programs that locate
themselves via /proc/self/exe find the dynamic linker instead [1].
Userspace cannot get this right on its own. PR_SET_MM_MAP's exe_fd is
gated on checkpoint_restore_ns_capable() in the caller's own user
namespace - that is how CRIU restores an exe link - so the ability to
retarget mm->exe_file is not what this adds. What userspace cannot do
is have the link be right from the first instruction. Credentials are
unaffected either way: they still derive from the interpreter unless
'C' says otherwise.
bprm->executable is the file execve() access-checked and kept open for
AT_EXECFD. It is already the file would_dump() bases the dumpability
decision on and the file bprm->execfd_creds derives credentials from.
Label mm->exe_file with it when the dispatch is transparent and the
identity is correct from the start. The label names precisely the file
the caller passed to execve().
Write-denial moves along with the label. Rather than tracking per mode
who still owes a release, the denial do_open_execat() took stays on
bprm->executable until the file is handed over. begin_new_exec() drops
it right before installing the descriptor - set_mm_exe_file() has taken
its own denial on the identity file by then - and free_bprm() releases
an unconsumed executable with do_close_execat() like the other exec
files. For a transparent dispatch the result is exact parity with a
direct execution: a concurrently written binary fails execve() with
-ETXTBSY at open and a running one cannot be opened for writing. The
interpreter consequently is not exe-pinned and matches the role it has
in a native PT_INTERP exec. A classic execfd dispatch now keeps the
binary write-denied until the exec completes rather than only until the
interpreter swap; the difference is confined to the exec itself.
Nothing sets BINPRM_FLAGS_TRANSPARENT_INTERP yet; the transparent
dispatch machinery in binfmt_misc follows and raises it from birth, so
the label and the aux vector bit that announces it appear together.
Link: https://inbox.sourceware.org/libc-alpha/87ik6fymha.fsf@oldenburg.str.redhat.com [1]
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-9-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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A transparent binfmt_misc dispatch hands the binary to the interpreter
through AT_EXECFD and leaves the argument vector exactly as the caller
built it. The loader on the receiving end has to know which contract it
got.
On the classic 'O'/'C' entries the binary's path is spliced into the
argument vector and the loader consumes arguments. In transparent mode
nothing was spliced and argv belongs entirely to the program. This
cannot be inferred from AT_EXECFD alone. Raise a new AT_FLAGS bit
following the AT_FLAGS_PRESERVE_ARGV0 precedent added for qemu-user in
commit 2347961b11d4 ("binfmt_misc: pass binfmt_misc flags to the
interpreter").
The bit also announces that mm->exe_file names the binary rather than
the interpreter (added in the next commit). A loader that sees the bit
may finish the identity polish by fixing up AT_PHDR/AT_ENTRY/AT_BASE in
saved_auxv and fix the code/data markers via one uncapped PR_SET_MM_MAP
once it has mapped the binary. I've got glibc patches for this as well
but it's useful for any loader.
BINPRM_FLAGS_TRANSPARENT_INTERP carries the mode from binfmt_misc to the
ELF loaders. Both had their own copy of the AT_FLAGS translation, so
give them one bprm_at_flags() to share instead of a second copy that can
drift. Nothing sets the bprm flag yet.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-8-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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The test reports its own pass and fail lines, returns a bare 4 for
KSFT_SKIP and runs both cases in one process, so a failure in the first
takes the second with it. It also open-codes the register, unregister,
file-copy and mount helpers that the tests for the upcoming transparent
and loader dispatch modes need again.
Convert it to the kselftest harness: a fixture for the common setup and
teardown, one TEST_F per case so each is reported and isolated
separately, and SKIP() for the root, BTF and binfmt_misc preconditions.
Move the helpers to a shared header on the way, with the register
helper preserving the write's errno so a caller can tell a rejected
flag combination (EINVAL) from a kernel that does not know the flag at
all. The synthetic ELF header gains an e_machine argument and uses the
elf.h constants instead of open-coded numbers.
The fixture no longer mounts bpffs. The handler is attached with
bpf_map__attach_struct_ops() and nothing is ever pinned, the mount was
carried along from a bpftool-based draft. The bpf objects are compiled
with -DBPF_NO_KFUNC_PROTOTYPES - the guard bpftool emits for exactly
this - instead of sed'ing the prototypes out of the generated
vmlinux.h. And the config fragment records the options the binfmt_misc
tests need so a merge-config kernel can run them.
No change in what is tested.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-7-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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When the format search stages an interpreter exec_binprm() swaps it
in and releases the file it replaces. Dropping the write denial the
open took is done manually ahead of both release paths. The one path
that keeps the file silently relies on it not being called.
Let's just use do_close_execat() on the two paths that release the file
and drop the denial explicitly on the one that does not.
No functional change.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-6-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Opening the interpreter is a property of the matched entry: an 'F' entry
hands out a clone of the file it pre-opened at registration time, any
other entry opens the selected path. Give that its own helper instead of
an if/else in the middle of load_misc_binary(), and let it fail early
rather than carrying an ERR_PTR through the successful branch.
Building the interpreter's argument vector is the bulk of what remains
and the one part of load_misc_binary() that is specific to the classic
dispatch. Move it into its own helper too, so the dispatch reads as what
it is: pick a handler, pick an interpreter, build the invocation, open
it.
No functional change.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-5-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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A static entry fixes its invocation flags at registration. A 'B' entry's
load program picks them per exec. Since load_misc_binary() branches on
which kind of entry matched and then applies the two flag sets side by
side every flag is handled twice and each new one has to be added to
both arms.
Translate the 'B' flags into the entry flags they mirror and let the
dispatch act on a single set of flags. The boolean the two arms
communicated 'P' can be removed.
No functional change.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-4-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Every flag character of the register string is spelled out three
times: in the parser, in the entry's /proc output and in the
delimiter blacklist that keeps a flag character from sending the flag
scan off the end of the buffer. The three lists have to agree, and
each new flag has to be added to all of them.
Describe a flag once - character, entry flag, implied flags and a
description for the registration debug output - and drive all three
from the table.
While at it, express the "a 'B' entry carries no flags" check as what
it is, an empty flags field, rather than as a fourth list of every
flag character. Equivalent: the check runs right after
check_special_flags(), which advances past exactly the flag
characters it consumed and sets exactly their flags.
No functional change.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-3-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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The general usage trails the bpf-backed handlers section and therefore
reads as part of it. It predates that section and applies to binfmt_misc
as a whole.
Move it back up so the handler section ends where the file does.
Upcoming sections describing the transparent and loader dispatch modes
append after it without swallowing the general prose again.
Pure text move, no content changes.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-2-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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A 'C' entry computes the credentials from the matched binary instead of
from the interpreter. So a set*id binary hands its credentials to
whatever the entry names as its interpreter.
Without 'F' that interpreter is not opened until the exec happens and
open_exec() resolves the path relative to the current working directory.
The working directory at that point belongs to whoever runs the binary
not to whoever registered the entry. So :x:M::\x7fELF::interp:C lets
every user who execs a matching set*id binary from a directory they
control run their own interp with that binary's credentials.
A relative interpreter has no sensible use here to begin with. The
registering task cannot know what the working directory will be. Make
the register string reject the combination at registration time.
This does refuse register strings that used to be accepted. The 'F' flag
covers the case where the interpreter really is meant to be resolved in
the registrant's context, and it resolves it once, at registration.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-1-e57866e4ae0f@kernel.org
Reviewed-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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Christian Brauner <brauner@kernel.org> says:
binfmt_misc: bpf-backed binary type handlers
This is a POC for the nix people and Farid and Eric in particular. I
would take my hands off the wheel now that I POCed this and hand it to
Farid if he likes to take it forward.
VL;MR (very long, must read):
For a while now Farid has been trying to make relocatable, hermetic
binaries (think Nix-style store layouts) work without patchelf tricks
or wrapper scripts. For such binaries the right dynamic loader can only
be determined relative to the location of the binary itself, which
neither PT_INTERP nor a fixed binfmt_misc interpreter string can
express.
The first attempt was $ORIGIN expansion in PT_INTERP [1]. I pushed back
on that. Userspace guards $ORIGIN behind AT_SECURE so the kernel would
have to make the used loader depend on the type of binary, LSMs would
need a say, it changes long-standing behavior in ways that are ripe for
loader injection attacks, and bprm->file may not have a usable path at
all (memfds, deleted files, unresolvable paths). Making the kernel
splice bprm->file back together with PT_INTERP is terrible. The second
attempt was a pluggable ELF interpreter loader registry [2] which would
mean actual kernel modules for custom binary formats. Also no.
binfmt_misc was invented to kill exactly this horrendous past.
What I suggested instead [3] was to put this where delegating binary
formats to userspace already lives: binfmt_misc. The only things
binfmt_misc cannot do today are matching programmatically and computing
the interpreter per binary instead of using a fixed string recorded at
registration time. Farid prototyped that with an eBPF program [4] and
it turned out quite workable, but the prototype ran a SOCKET_FILTER
program over bprm->buf, added a new helper to the frozen uapi helper
list, and returned the computed path through per-CPU memory.
This series is the proposal turned into what I think the bpf side
{c,sh}ould actually look like. It is a POC: it builds, the selftests
pass, and the design is what I want to discuss. The selftests are
Farid's from his v2 posting, adapted to the contract below.
A handler is an instance of the new binfmt_misc_ops struct_ops with a
name and two ops:
struct binfmt_misc_ops {
bool (*match)(struct linux_binprm *bprm);
int (*load)(struct linux_binprm *bprm);
char name[BINFMT_MISC_OPS_NAME_MAX];
};
Both programs receive the bprm as a trusted BTF pointer and both are
sleepable. The match program decides from the entry lookup walk whether
the handler applies, under the same rules as magic matching:
registration order, first match wins. It is not limited to the
prefetched 256 bytes in bprm->buf: it can read arbitrary file content
through bpf_dynptr_from_file(), e.g. to find an ELF interpreter
segment at whatever offset it sits. That is what makes multiple
independent handlers workable at all - a handler that cannot read the
file would have to match broadly and reject from its load program,
stealing the binaries of every handler registered after it. To make
this safe the entry walk becomes an SRCU read-side section. The load
program of the matched handler then selects the interpreter, reading
the file the same way and resolving the binary's location via
bpf_path_d_path() on &bprm->file->f_path. That also solves the
prototype's limitation of only seeing the first 256 bytes of the file.
Selecting is the load program's privilege: the verifier rejects the
selection kfuncs in match, keyed off the struct_ops member a program
attaches to. A match commits the exec to the handler: a failing load
fails the exec instead of falling through to later entries, with
-ENOEXEC handing over to the remaining binary formats, so the walk is
never left and re-entered.
The genuinely new piece of bpf surface is a small family of kfuncs:
int bpf_binprm_set_interp(struct linux_binprm *bprm,
const char *path, size_t path__sz);
int bpf_binprm_set_interp_arg(struct linux_binprm *bprm,
const char *arg, size_t arg__sz);
int bpf_binprm_set_flags(struct linux_binprm *bprm,
enum bpf_binprm_flags flags);
staging the selected interpreter, an optional single argument for it
(the slot the optional argument of a #! interpreter line has), and the
per-exec invocation flags - 'P', 'C' and 'O' equivalents. Selection
cannot go through bprm_change_interp() directly because
load_misc_binary() copies bprm->interp into argv[1] after the program
ran, hence the staging fields added in patch 1.
Registering (attaching) the struct_ops map publishes the handler under
its name in a registry keyed by the registering task's user namespace.
Activation reuses the existing text interface with a new 'B' type where
the interpreter field carries the handler name - it consistently names
whoever supplies the interpreter - and offset, magic, and mask must be
empty:
echo ':origin:B::::nix:' > /proc/sys/fs/binfmt_misc/register
This keeps the existing permission and namespacing model completely
intact. Activating a handler requires the same write access to a
binfmt_misc instance as any other registration, a container mounting
its own instance escapes the host's entries exactly as before, and
shadowing e.g. all ELF binaries takes the same privilege as a static
'M' entry matching \x7fELF does today.
The only novelty is that matching becomes programmable. Handler lookup
walks the user namespace hierarchy upwards, mirroring how binfmt_misc
instances themselves are resolved, so a handler registered on the host
can be activated from a container's own instance without being forced
upon it.
The computed interpreter is opened with open_exec() under the caller's
credentials and goes through the full LSM vetting as the next binprm
level, exactly like a statically registered interpreter, so the program
cannot widen access. It only ever redirects the caller to something the
caller could exec anyway.
A 'B' entry carries no flags in the register string: the load program
chooses the invocation flags per exec through bpf_binprm_set_flags()
instead. BPF_BINPRM_PRESERVE_ARGV0, BPF_BINPRM_CREDENTIALS and
BPF_BINPRM_EXECFD keep the static 'P', 'C' and 'O' semantics -
BPF_BINPRM_CREDENTIALS honors the matched binary's suid bits exactly
as a static 'C' entry does, with the setuid transition gated by
vfsuid_has_mapping() in the caller's user namespace either way, which
makes 'B' handlers usable for a per-binary loader over setuid
binaries. 'F' (pre-open a fixed interpreter) is rejected: a 'B' entry
has no fixed interpreter. AT_EXECVE_CHECK never invokes programs and
interpreter chains stay capped by the usual ELOOP depth.
A handler for the Nix case then looks roughly like:
SEC("struct_ops.s/match")
bool BPF_PROG(nix_match, struct linux_binprm *bprm)
{
return !bpf_strncmp(bprm->buf, 4, "\x7f" "ELF");
}
SEC("struct_ops.s/load")
int BPF_PROG(nix_load, struct linux_binprm *bprm)
{
char path[256];
long n;
n = bpf_path_d_path(&bprm->file->f_path, path, sizeof(path));
if (n < 0)
return n;
/* derive the loader location from the binary's path */
return bpf_binprm_set_interp(bprm, path, sizeof(path));
}
SEC(".struct_ops.link")
struct binfmt_misc_ops nix = {
.match = (void *)nix_match,
.load = (void *)nix_load,
.name = "nix",
};
Farid, this should slot underneath your qemu demo from [4] with the
program ported to struct_ops. Feel free to take it from here.
[1]: https://lore.kernel.org/20260622043934.179879-1-farid.m.zakaria@gmail.com
[2]: https://lore.kernel.org/20260702214247.1253741-1-farid.m.zakaria@gmail.com
[3]: https://lore.kernel.org/20260703-meditation-ratsuchende-moratorium-9ecdf1f3f8bb@brauner
[4]: https://lore.kernel.org/20260704211409.1978485-1-farid.m.zakaria@gmail.com
* patches from https://patch.msgid.link/20260714-work-bpf-binfmt_misc-v2-0-57b7529c002c@kernel.org:
selftests/exec: add binfmt_misc bpf-backed handler test
binfmt_misc: let a bpf handler choose the invocation flags per exec
binfmt_misc: let bpf handlers pass an argument to the interpreter
bpf: allow fs kfuncs for binfmt_misc_ops programs
binfmt_misc: wire up bpf-backed 'B' entries
binfmt_misc: let the entry lookup walk sleep
binfmt_misc: add binfmt_misc_ops bpf struct_ops
exec: stash bpf-selected interpreter state in struct linux_binprm
Link: https://patch.msgid.link/20260714-work-bpf-binfmt_misc-v2-0-57b7529c002c@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
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