get_stashed_dentry() tries to optimistically retrieve a stashed dentry
from a provided location.  It needs to ensure to hold rcu lock before it
dereference the stashed location to prevent UAF issues.  Use
rcu_dereference() instead of READ_ONCE() it's effectively equivalent
with some lockdep bells and whistles and it communicates clearly that
this expects rcu protection.

Link: https://lore.kernel.org/r/20240906-vfs-hotfix-5959800ffa68@brauner
Fixes: 07fd7c329839 ("libfs: add path_from_stashed()")
Reported-by: syzbot+f82b36bffae7ef78b6a7@syzkaller.appspotmail.com
Fixes: syzbot+f82b36bffae7ef78b6a7@syzkaller.appspotmail.com
Reported-by: syzbot+cbe4b96e1194b0e34db6@syzkaller.appspotmail.com
Fixes: syzbot+cbe4b96e1194b0e34db6@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

After we switch tmpfs dir operations from simple_dir_operations to
simple_offset_dir_operations, every rename happened will fill new dentry
to dest dir's maple tree(&SHMEM_I(inode)->dir_offsets->mt) with a free
key starting with octx->newx_offset, and then set newx_offset equals to
free key + 1. This will lead to infinite readdir combine with rename
happened at the same time, which fail generic/736 in xfstests(detail show
as below).

1. create 5000 files(1 2 3...) under one dir
2. call readdir(man 3 readdir) once, and get one entry
3. rename(entry, "TEMPFILE"), then rename("TEMPFILE", entry)
4. loop 2~3, until readdir return nothing or we loop too many
   times(tmpfs break test with the second condition)

We choose the same logic what commit 9b378f6ad48cf ("btrfs: fix infinite
directory reads") to fix it, record the last_index when we open dir, and
do not emit the entry which index >= last_index. The file->private_data
now used in offset dir can use directly to do this, and we also update
the last_index when we llseek the dir file.

Fixes: a2e459555c5f ("shmem: stable directory offsets")
Signed-off-by: yangerkun <yangerkun@huawei.com>
Link: https://lore.kernel.org/r/20240731043835.1828697-1-yangerkun@huawei.com
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
[brauner: only update last_index after seek when offset is zero like Jan suggested]
Signed-off-by: Christian Brauner <brauner@kernel.org>

generic_ci_match can be used by case-insensitive filesystems to compare
strings under lookup with dirents in a case-insensitive way.  This
function is currently reimplemented by each filesystem supporting
casefolding, so this reduces code duplication in filesystem-specific
code.

[eugen.hristev@collabora.com: rework to first test the exact match, cleanup
and add error message]

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Link: https://lore.kernel.org/r/20240606073353.47130-4-eugen.hristev@collabora.com
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

When renaming onto an existing directory entry, user space expects
the replacement entry to have the same directory offset as the
original one.

Link: https://gitlab.alpinelinux.org/alpine/aports/-/issues/15966
Fixes: a2e459555c5f ("shmem: stable directory offsets")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20240415152057.4605-4-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

I'm about to fix a tmpfs rename bug that requires the use of
internal simple_offset helpers that are not available in mm/shmem.c

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20240415152057.4605-3-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

User space expects the replacement (old) directory entry to have
the same directory offset after the rename.

Suggested-by: Christian Brauner <brauner@kernel.org>
Fixes: a2e459555c5f ("shmem: stable directory offsets")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20240415152057.4605-2-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

As Linus suggested this enables pidfs unconditionally. A key property to
retain is the ability to compare pidfds by inode number (cf. [1]).
That's extremely helpful just as comparing namespace file descriptors by
inode number is. They are used in a variety of scenarios where they need
to be compared, e.g., when receiving a pidfd via SO_PEERPIDFD from a
socket to trivially authenticate a the sender and various other
use-cases.

For 64bit systems this is pretty trivial to do. For 32bit it's slightly
more annoying as we discussed but we simply add a dumb ida based
allocator that gets used on 32bit. This gives the same guarantees about
inode numbers on 64bit without any overflow risk. Practically, we'll
never run into overflow issues because we're constrained by the number
of processes that can exist on 32bit and by the number of open files
that can exist on a 32bit system. On 64bit none of this matters and
things are very simple.

If 32bit also needs the uniqueness guarantee they can simply parse the
contents of /proc/<pid>/fd/<nr>. The uniqueness guarantees have a
variety of use-cases. One of the most obvious ones is that they will
make pidfiles (or "pidfdfiles", I guess) reliable as the unique
identifier can be placed into there that won't be reycled. Also a
frequent request.

Note, I took the chance and simplified path_from_stashed() even further.
Instead of passing the inode number explicitly to path_from_stashed() we
let the filesystem handle that internally. So path_from_stashed() ends
up even simpler than it is now. This is also a good solution allowing
the cleanup code to be clean and consistent between 32bit and 64bit. The
cleanup path in prepare_anon_dentry() is also switched around so we put
the inode before the dentry allocation. This means we only have to call
the cleanup handler for the filesystem's inode data once and can rely
->evict_inode() otherwise.

Aside from having to have a bit of extra code for 32bit it actually ends
up a nice cleanup for path_from_stashed() imho.

Tested on both 32 and 64bit including error injection.

Link: https://github.com/systemd/systemd/pull/31713 [1]
Link: https://lore.kernel.org/r/20240312-dingo-sehnlich-b3ecc35c6de7@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull file locking updates from Christian Brauner:
 "A few years ago struct file_lock_context was added to allow for
  separate lists to track different types of file locks instead of using
  a singly-linked list for all of them.

  Now leases no longer need to be tracked using struct file_lock.
  However, a lot of the infrastructure is identical for leases and locks
  so separating them isn't trivial.

  This splits a group of fields used by both file locks and leases into
  a new struct file_lock_core. The new core struct is embedded in struct
  file_lock. Coccinelle was used to convert a lot of the callers to deal
  with the move, with the remaining 25% or so converted by hand.

  Afterwards several internal functions in fs/locks.c are made to work
  with struct file_lock_core. Ultimately this allows to split struct
  file_lock into struct file_lock and struct file_lease. The file lease
  APIs are then converted to take struct file_lease"

* tag 'vfs-6.9.file' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (51 commits)
  filelock: fix deadlock detection in POSIX locking
  filelock: always define for_each_file_lock()
  smb: remove redundant check
  filelock: don't do security checks on nfsd setlease calls
  filelock: split leases out of struct file_lock
  filelock: remove temporary compatibility macros
  smb/server: adapt to breakup of struct file_lock
  smb/client: adapt to breakup of struct file_lock
  ocfs2: adapt to breakup of struct file_lock
  nfsd: adapt to breakup of struct file_lock
  nfs: adapt to breakup of struct file_lock
  lockd: adapt to breakup of struct file_lock
  fuse: adapt to breakup of struct file_lock
  gfs2: adapt to breakup of struct file_lock
  dlm: adapt to breakup of struct file_lock
  ceph: adapt to breakup of struct file_lock
  afs: adapt to breakup of struct file_lock
  9p: adapt to breakup of struct file_lock
  filelock: convert seqfile handling to use file_lock_core
  filelock: convert locks_translate_pid to take file_lock_core
  ...

Pull pdfd updates from Christian Brauner:

 - Until now pidfds could only be created for thread-group leaders but
   not for threads. There was no technical reason for this. We simply
   had no users that needed support for this. Now we do have users that
   need support for this.

   This introduces a new PIDFD_THREAD flag for pidfd_open(). If that
   flag is set pidfd_open() creates a pidfd that refers to a specific
   thread.

   In addition, we now allow clone() and clone3() to be called with
   CLONE_PIDFD | CLONE_THREAD which wasn't possible before.

   A pidfd that refers to an individual thread differs from a pidfd that
   refers to a thread-group leader:

    (1) Pidfds are pollable. A task may poll a pidfd and get notified
        when the task has exited.

        For thread-group leader pidfds the polling task is woken if the
        thread-group is empty. In other words, if the thread-group
        leader task exits when there are still threads alive in its
        thread-group the polling task will not be woken when the
        thread-group leader exits but rather when the last thread in the
        thread-group exits.

        For thread-specific pidfds the polling task is woken if the
        thread exits.

    (2) Passing a thread-group leader pidfd to pidfd_send_signal() will
        generate thread-group directed signals like kill(2) does.

        Passing a thread-specific pidfd to pidfd_send_signal() will
        generate thread-specific signals like tgkill(2) does.

        The default scope of the signal is thus determined by the type
        of the pidfd.

        Since use-cases exist where the default scope of the provided
        pidfd needs to be overriden the following flags are added to
        pidfd_send_signal():

         - PIDFD_SIGNAL_THREAD
           Send a thread-specific signal.

         - PIDFD_SIGNAL_THREAD_GROUP
           Send a thread-group directed signal.

         - PIDFD_SIGNAL_PROCESS_GROUP
           Send a process-group directed signal.

        The scope change will only work if the struct pid is actually
        used for this scope.

        For example, in order to send a thread-group directed signal the
        provided pidfd must be used as a thread-group leader and
        similarly for PIDFD_SIGNAL_PROCESS_GROUP the struct pid must be
        used as a process group leader.

 - Move pidfds from the anonymous inode infrastructure to a tiny pseudo
   filesystem. This will unblock further work that we weren't able to do
   simply because of the very justified limitations of anonymous inodes.
   Moving pidfds to a tiny pseudo filesystem allows for statx on pidfds
   to become useful for the first time. They can now be compared by
   inode number which are unique for the system lifetime.

   Instead of stashing struct pid in file->private_data we can now stash
   it in inode->i_private. This makes it possible to introduce concepts
   that operate on a process once all file descriptors have been closed.
   A concrete example is kill-on-last-close. Another side-effect is that
   file->private_data is now freed up for per-file options for pidfds.

   Now, each struct pid will refer to a different inode but the same
   struct pid will refer to the same inode if it's opened multiple
   times. In contrast to now where each struct pid refers to the same
   inode.

   The tiny pseudo filesystem is not visible anywhere in userspace
   exactly like e.g., pipefs and sockfs. There's no lookup, there's no
   complex inode operations, nothing. Dentries and inodes are always
   deleted when the last pidfd is closed.

   We allocate a new inode and dentry for each struct pid and we reuse
   that inode and dentry for all pidfds that refer to the same struct
   pid. The code is entirely optional and fairly small. If it's not
   selected we fallback to anonymous inodes. Heavily inspired by nsfs.

   The dentry and inode allocation mechanism is moved into generic
   infrastructure that is now shared between nsfs and pidfs. The
   path_from_stashed() helper must be provided with a stashing location,
   an inode number, a mount, and the private data that is supposed to be
   used and it will provide a path that can be passed to dentry_open().

   The helper will try retrieve an existing dentry from the provided
   stashing location. If a valid dentry is found it is reused. If not a
   new one is allocated and we try to stash it in the provided location.
   If this fails we retry until we either find an existing dentry or the
   newly allocated dentry could be stashed. Subsequent openers of the
   same namespace or task are then able to reuse it.

 - Currently it is only possible to get notified when a task has exited,
   i.e., become a zombie and userspace gets notified with EPOLLIN. We
   now also support waiting until the task has been reaped, notifying
   userspace with EPOLLHUP.

 - Ensure that ESRCH is reported for getfd if a task is exiting instead
   of the confusing EBADF.

 - Various smaller cleanups to pidfd functions.

* tag 'vfs-6.9.pidfd' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (23 commits)
  libfs: improve path_from_stashed()
  libfs: add stashed_dentry_prune()
  libfs: improve path_from_stashed() helper
  pidfs: convert to path_from_stashed() helper
  nsfs: convert to path_from_stashed() helper
  libfs: add path_from_stashed()
  pidfd: add pidfs
  pidfd: move struct pidfd_fops
  pidfd: allow to override signal scope in pidfd_send_signal()
  pidfd: change pidfd_send_signal() to respect PIDFD_THREAD
  signal: fill in si_code in prepare_kill_siginfo()
  selftests: add ESRCH tests for pidfd_getfd()
  pidfd: getfd should always report ESRCH if a task is exiting
  pidfd: clone: allow CLONE_THREAD | CLONE_PIDFD together
  pidfd: exit: kill the no longer used thread_group_exited()
  pidfd: change do_notify_pidfd() to use __wake_up(poll_to_key(EPOLLIN))
  pid: kill the obsolete PIDTYPE_PID code in transfer_pid()
  pidfd: kill the no longer needed do_notify_pidfd() in de_thread()
  pidfd_poll: report POLLHUP when pid_task() == NULL
  pidfd: implement PIDFD_THREAD flag for pidfd_open()
  ...

Merge case-insensitive updates from Gabriel Krisman Bertazi:

- Patch case-insensitive lookup by trying the case-exact comparison
  first, before falling back to costly utf8 casefolded comparison.

- Fix to forbid using a case-insensitive directory as part of an
  overlayfs mount.

- Patchset to ensure d_op are set at d_alloc time for fscrypt and
  casefold volumes, ensuring filesystem dentries will all have the
  correct ops, whether they come from a lookup or not.

* tag 'for-next-6.9' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/krisman/unicode:
  libfs: Drop generic_set_encrypted_ci_d_ops
  ubifs: Configure dentry operations at dentry-creation time
  f2fs: Configure dentry operations at dentry-creation time
  ext4: Configure dentry operations at dentry-creation time
  libfs: Add helper to choose dentry operations at mount-time
  libfs: Merge encrypted_ci_dentry_ops and ci_dentry_ops
  fscrypt: Drop d_revalidate once the key is added
  fscrypt: Drop d_revalidate for valid dentries during lookup
  fscrypt: Factor out a helper to configure the lookup dentry
  ovl: Always reject mounting over case-insensitive directories
  libfs: Attempt exact-match comparison first during casefolded lookup

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