When we added mount_setattr() I added additional checks compared to the
legacy do_reconfigure_mnt() and do_change_type() helpers used by regular
mount(2). If that mount had a parent then verify that the caller and the
mount namespace the mount is attached to match and if not make sure that
it's an anonymous mount.

The real rootfs falls into neither category. It is neither an anoymous
mount because it is obviously attached to the initial mount namespace
but it also obviously doesn't have a parent mount. So that means legacy
mount(2) allows changing mount properties on the real rootfs but
mount_setattr(2) blocks this. I never thought much about this but of
course someone on this planet of earth changes properties on the real
rootfs as can be seen in [1].

Since util-linux finally switched to the new mount api in 2.39 not so
long ago it also relies on mount_setattr() and that surfaced this issue
when Fedora 39 finally switched to it. Fix this.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2256843
Link: https://lore.kernel.org/r/20240206-vfs-mount-rootfs-v1-1-19b335eee133@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reported-by: Karel Zak <kzak@redhat.com>
Cc: stable@vger.kernel.org # v5.12+
Signed-off-by: Christian Brauner <brauner@kernel.org>

Linus pointed out that there's error handling and naming issues in the
that we should rewrite:

* Perform the access checks for the buffer before actually doing any
  work instead of doing it during the iteration.
* Rename the arguments to listmount() and do_listmount() to clarify what
  the arguments are used for.
* Get rid of the pointless ctr variable and overflow checking.
* Get rid of the pointless speculation check.

Link: https://lore.kernel.org/r/CAHk-=wjh6Cypo8WC-McXgSzCaou3UXccxB+7PVeSuGR8AjCphg@mail.gmail.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Pull sysctl updates from Luis Chamberlain:
 "To help make the move of sysctls out of kernel/sysctl.c not incur a
  size penalty sysctl has been changed to allow us to not require the
  sentinel, the final empty element on the sysctl array. Joel Granados
  has been doing all this work.

  In the v6.6 kernel we got the major infrastructure changes required to
  support this. For v6.7 we had all arch/ and drivers/ modified to
  remove the sentinel. For v6.8-rc1 we get a few more updates for fs/
  directory only.

  The kernel/ directory is left but we'll save that for v6.9-rc1 as
  those patches are still being reviewed. After that we then can expect
  also the removal of the no longer needed check for procname == NULL.

  Let us recap the purpose of this work:

   - this helps reduce the overall build time size of the kernel and run
     time memory consumed by the kernel by about ~64 bytes per array

   - the extra 64-byte penalty is no longer inncurred now when we move
     sysctls out from kernel/sysctl.c to their own files

  Thomas Weißschuh also sent a few cleanups, for v6.9-rc1 we expect to
  see further work by Thomas Weißschuh with the constificatin of the
  struct ctl_table.

  Due to Joel Granados's work, and to help bring in new blood, I have
  suggested for him to become a maintainer and he's accepted. So for
  v6.9-rc1 I look forward to seeing him sent you a pull request for
  further sysctl changes. This also removes Iurii Zaikin as a maintainer
  as he has moved on to other projects and has had no time to help at
  all"

* tag 'sysctl-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux:
  sysctl: remove struct ctl_path
  sysctl: delete unused define SYSCTL_PERM_EMPTY_DIR
  coda: Remove the now superfluous sentinel elements from ctl_table array
  sysctl: Remove the now superfluous sentinel elements from ctl_table array
  fs: Remove the now superfluous sentinel elements from ctl_table array
  cachefiles: Remove the now superfluous sentinel element from ctl_table array
  sysclt: Clarify the results of selftest run
  sysctl: Add a selftest for handling empty dirs
  sysctl: Fix out of bounds access for empty sysctl registers
  MAINTAINERS: Add Joel Granados as co-maintainer for proc sysctl
  MAINTAINERS: remove Iurii Zaikin from proc sysctl

Pull btrfs updates from David Sterba:
 "There are no exciting changes for users, it's been mostly API
  conversions and some fixes or refactoring.

  The mount API conversion is a base for future improvements that would
  come with VFS. Metadata processing has been converted to folios, not
  yet enabling the large folios but it's one patch away once everything
  gets tested enough.

  Core changes:

   - convert extent buffers to folios:
      - direct API conversion where possible
      - performance can drop by a few percent on metadata heavy
        workloads, the folio sizes are not constant and the calculations
        add up in the item helpers
      - both regular and subpage modes
      - data cannot be converted yet, we need to port that to iomap and
        there are some other generic changes required

   - convert mount to the new API, should not be user visible:
      - options deprecated long time ago have been removed: inode_cache,
        recovery
      - the new logic that splits mount to two phases slightly changes
        timing of device scanning for multi-device filesystems
      - LSM options will now work (like for selinux)

   - convert delayed nodes radix tree to xarray, preserving the
     preload-like logic that still allows to allocate with GFP_NOFS

   - more validation of sysfs value of scrub_speed_max

   - refactor chunk map structure, reduce size and improve performance

   - extent map refactoring, smaller data structures, improved
     performance

   - reduce size of struct extent_io_tree, embedded in several
     structures

   - temporary pages used for compression are cached and attached to a
     shrinker, this may slightly improve performance

   - in zoned mode, remove redirty extent buffer tracking, zeros are
     written in case an out-of-order is detected and proper data are
     written to the actual write pointer

   - cleanups, refactoring, error message improvements, updated tests

   - verify and update branch name or tag

   - remove unwanted text"

* tag 'for-6.8-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux: (89 commits)
  btrfs: pass btrfs_io_geometry into btrfs_max_io_len
  btrfs: pass struct btrfs_io_geometry to set_io_stripe
  btrfs: open code set_io_stripe for RAID56
  btrfs: change block mapping to switch/case in btrfs_map_block
  btrfs: factor out block mapping for single profiles
  btrfs: factor out block mapping for RAID5/6
  btrfs: reduce scope of data_stripes in btrfs_map_block
  btrfs: factor out block mapping for RAID10
  btrfs: factor out block mapping for DUP profiles
  btrfs: factor out RAID1 block mapping
  btrfs: factor out block-mapping for RAID0
  btrfs: re-introduce struct btrfs_io_geometry
  btrfs: factor out helper for single device IO check
  btrfs: migrate btrfs_repair_io_failure() to folio interfaces
  btrfs: migrate eb_bitmap_offset() to folio interfaces
  btrfs: migrate various end io functions to folios
  btrfs: migrate subpage code to folio interfaces
  btrfs: migrate get_eb_page_index() and get_eb_offset_in_page() to folios
  btrfs: don't double put our subpage reference in alloc_extent_buffer
  btrfs: cleanup metadata page pointer usage
  ...

Pull vfs mount updates from Christian Brauner:
 "This contains the work to retrieve detailed information about mounts
  via two new system calls. This is hopefully the beginning of the end
  of the saga that started with fsinfo() years ago.

  The LWN articles in [1] and [2] can serve as a summary so we can avoid
  rehashing everything here.

  At LSFMM in May 2022 we got into a room and agreed on what we want to
  do about fsinfo(). Basically, split it into pieces. This is the first
  part of that agreement. Specifically, it is concerned with retrieving
  information about mounts. So this only concerns the mount information
  retrieval, not the mount table change notification, or the extended
  filesystem specific mount option work. That is separate work.

  Currently mounts have a 32bit id. Mount ids are already in heavy use
  by libmount and other low-level userspace but they can't be relied
  upon because they're recycled very quickly. We agreed that mounts
  should carry a unique 64bit id by which they can be referenced
  directly. This is now implemented as part of this work.

  The new 64bit mount id is exposed in statx() through the new
  STATX_MNT_ID_UNIQUE flag. If the flag isn't raised the old mount id is
  returned. If it is raised and the kernel supports the new 64bit mount
  id the flag is raised in the result mask and the new 64bit mount id is
  returned. New and old mount ids do not overlap so they cannot be
  conflated.

  Two new system calls are introduced that operate on the 64bit mount
  id: statmount() and listmount(). A summary of the api and usage can be
  found on LWN as well (cf. [3]) but of course, I'll provide a summary
  here as well.

  Both system calls rely on struct mnt_id_req. Which is the request
  struct used to pass the 64bit mount id identifying the mount to
  operate on. It is extensible to allow for the addition of new
  parameters and for future use in other apis that make use of mount
  ids.

  statmount() mimicks the semantics of statx() and exposes a set flags
  that userspace may raise in mnt_id_req to request specific information
  to be retrieved. A statmount() call returns a struct statmount filled
  in with information about the requested mount. Supported requests are
  indicated by raising the request flag passed in struct mnt_id_req in
  the @mask argument in struct statmount.

  Currently we do support:

   - STATMOUNT_SB_BASIC:
     Basic filesystem info

   - STATMOUNT_MNT_BASIC
     Mount information (mount id, parent mount id, mount attributes etc)

   - STATMOUNT_PROPAGATE_FROM
     Propagation from what mount in current namespace

   - STATMOUNT_MNT_ROOT
     Path of the root of the mount (e.g., mount --bind /bla /mnt returns /bla)

   - STATMOUNT_MNT_POINT
     Path of the mount point (e.g., mount --bind /bla /mnt returns /mnt)

   - STATMOUNT_FS_TYPE
     Name of the filesystem type as the magic number isn't enough due to submounts

  The string options STATMOUNT_MNT_{ROOT,POINT} and STATMOUNT_FS_TYPE
  are appended to the end of the struct. Userspace can use the offsets
  in @fs_type, @mnt_root, and @mnt_point to reference those strings
  easily.

  The struct statmount reserves quite a bit of space currently for
  future extensibility. This isn't really a problem and if this bothers
  us we can just send a follow-up pull request during this cycle.

  listmount() is given a 64bit mount id via mnt_id_req just as
  statmount(). It takes a buffer and a size to return an array of the
  64bit ids of the child mounts of the requested mount. Userspace can
  thus choose to either retrieve child mounts for a mount in batches or
  iterate through the child mounts. For most use-cases it will be
  sufficient to just leave space for a few child mounts. But for big
  mount tables having an iterator is really helpful. Iterating through a
  mount table works by setting @param in mnt_id_req to the mount id of
  the last child mount retrieved in the previous listmount() call"

Link: https://lwn.net/Articles/934469 [1]
Link: https://lwn.net/Articles/829212 [2]
Link: https://lwn.net/Articles/950569 [3]

* tag 'vfs-6.8.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  add selftest for statmount/listmount
  fs: keep struct mnt_id_req extensible
  wire up syscalls for statmount/listmount
  add listmount(2) syscall
  statmount: simplify string option retrieval
  statmount: simplify numeric option retrieval
  add statmount(2) syscall
  namespace: extract show_path() helper
  mounts: keep list of mounts in an rbtree
  add unique mount ID

This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which
will reduce the overall build time size of the kernel and run time
memory bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)

Remove sentinel elements ctl_table struct. Special attention was placed in
making sure that an empty directory for fs/verity was created when
CONFIG_FS_VERITY_BUILTIN_SIGNATURES is not defined. In this case we use the
register sysctl call that expects a size.

Signed-off-by: Joel Granados <j.granados@samsung.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

We already communicate to filesystems when a remount request comes from
the old mount API as some filesystems choose to implement different
behavior in the new mount API than the old mount API to e.g., take the
chance to fix significant API bugs. Allow the same for regular mount
requests.

Fixes: b330966f79fb ("fuse: reject options on reconfigure via fsconfig(2)")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Make it extensible so that we have the liberty to reuse it in future
mount-id based apis. Treat zero size as the first published struct.

Signed-off-by: Christian Brauner <brauner@kernel.org>

Add way to query the children of a particular mount.  This is a more
flexible way to iterate the mount tree than having to parse
/proc/self/mountinfo.

Lookup the mount by the new 64bit mount ID. If a mount needs to be
queried based on path, then statx(2) can be used to first query the
mount ID belonging to the path.

Return an array of new (64bit) mount ID's. Without privileges only
mounts are listed which are reachable from the task's root.

Folded into this patch are several later improvements. Keeping them
separate would make the history pointlessly confusing:

* Recursive listing of mounts is the default now (cf. [1]).
* Remove explicit LISTMOUNT_UNREACHABLE flag (cf. [1]) and fail if mount
  is unreachable from current root. This also makes permission checking
  consistent with statmount() (cf. [3]).
* Start listing mounts in unique mount ID order (cf. [2]) to allow
  continuing listmount() from a midpoint.
* Allow to continue listmount(). The @request_mask parameter is renamed
  and to @param to be usable by both statmount() and listmount().
  If @param is set to a mount id then listmount() will continue listing
  mounts from that id on. This allows listing mounts in multiple
  listmount invocations without having to resize the buffer. If @param
  is zero then the listing starts from the beginning (cf. [4]).
* Don't return EOVERFLOW, instead return the buffer size which allows to
  detect a full buffer as well (cf. [4]).

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20231025140205.3586473-6-mszeredi@redhat.com
Reviewed-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/20231128160337.29094-2-mszeredi@redhat.com [1] (folded)
Link: https://lore.kernel.org/r/20231128160337.29094-3-mszeredi@redhat.com [2] (folded)
Link: https://lore.kernel.org/r/20231128160337.29094-4-mszeredi@redhat.com [3] (folded)
Link: https://lore.kernel.org/r/20231128160337.29094-5-mszeredi@redhat.com [4] (folded)
[Christian Brauner <brauner@kernel.org>: various smaller fixes]
Signed-off-by: Christian Brauner <brauner@kernel.org>

The previous code was a bit too clever for what we currently support.

A few minor changes:

* Avoid indirect function calls and use a simple switch statement. We
  really only have three cases to handle so it's not like it's massively
  complex. We can switch to something more elaborate should we introduce
  more complex options.
* Defer all copy_to_user() calls until after we've given up namespace
  semaphore.
  On kernels with userfaultfd it's possible to abuse copy_from/to_user()
  calls to indefinitely block on page faults. That's usually a
  privileged operation but may be made available to unprivileged users.

  Independent of userfaultfd it's better to not do all the
  copy_to_user() work while holding namespace semaphore. Instead collect
  the information and then copy it out after we've given up all locks.
* This also folds a change from Arnd to reduce the stack size in
  prepare_kstatmount() to avoid warning such as:

  fs/namespace.c:4995:1: error: stack frame size (1536) exceeds limit (1024) in '__se_sys_statmount' [-Werror,-Wframe-larger-than]
   4995 | SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,

Reviewed-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/20231213090015.518044-1-arnd@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>