Re: [PATCH v2 2/2] audit: fix recursive locking deadlock in audit_dupe_exe()

[Paul Moore <paul@paul-moore.com>]

On May 13, 2026 Ricardo Robaina <rrobaina@redhat.com> wrote:
> 
> A deadlock occurs in the audit subsystem when duplicating
> executable-related rules.
> 
> When a file is moved (e.g., via do_renameat2()), the VFS layer locks
> the parent directory (I_MUTEX_PARENT), which synchronously triggers an
> fsnotify_move event. If an existing executable audit rule matches the
> file being moved, the audit subsystem catches this event and calls
> audit_dupe_exe() to duplicate the watch and update the rule. Then,
> audit_alloc_mark() would call kern_path_parent() to resolve the path,
> leading to a blind attempt to acquire the exact same I_MUTEX_PARENT lock
> already held by the task, resulting in the following recursive locking
> deadlock:
> 
>  ============================================
>  WARNING: possible recursive locking detected
>  6.12.0-55.27.1.el10_0.x86_64+debug #1 Not tainted
>  --------------------------------------------
>  mv/5099 is trying to acquire lock:
>  ffff888132845358 (&inode->i_sb->s_type->i_mutex_dir_key/1){+.+.}-{3:3},
>  at: __kern_path_locked+0x10a/0x2f0
> 
>  but task is already holding lock:
>  ffff888132846b58 (&inode->i_sb->s_type->i_mutex_dir_key/1){+.+.}-{3:3},
>  at: lock_two_directories+0x13f/0x2b0
> 
>  other info that might help us debug this:
>   Possible unsafe locking scenario:
> 
>         CPU0
>         ----
>    lock(&inode->i_sb->s_type->i_mutex_dir_key/1);
>    lock(&inode->i_sb->s_type->i_mutex_dir_key/1);
> 
>   *** DEADLOCK ***
> 
>   May be due to missing lock nesting notation
> 
>   6 locks held by mv/5099:
>   #0: ffff888112a9c440 (sb_writers#13)
>   at: do_renameat2+0x34c/0xbc0
>   #1: ffff888112a9c790 (&type->s_vfs_rename_key#3)
>   at: do_renameat2+0x415/0xbc0
>   #2: ffff888132846b58 (&inode->i_sb->s_type->i_mutex_dir_key/1)
>   at: lock_two_directories+0x13f/0x2b0
>   #3: ffff888132845358 (&inode->i_sb->s_type->i_mutex_dir_key/5)
>   at: lock_two_directories+0x175/0x2b0
>   #4: ffffffffb3a1fb10 (&fsnotify_mark_srcu)
>   at: fsnotify+0x454/0x28a0
>   #5: ffffffffaf886230 (audit_filter_mutex)
>   at: audit_update_watch+0x36/0x11e0
> 
>  stack backtrace:
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0x6f/0xb0
>   print_deadlock_bug.cold+0xbd/0xca
>   validate_chain+0x83a/0xf00
>   __lock_acquire+0xcac/0x1d20
>   lock_acquire.part.0+0x11b/0x360
>   down_write_nested+0x9f/0x230
>   __kern_path_locked+0x10a/0x2f0
>   kern_path_locked+0x26/0x40
>   audit_alloc_mark+0xfb/0x4f0
>   audit_dupe_exe+0x6c/0xe0
>   audit_dupe_rule+0x6c2/0xc00
>   audit_update_watch+0x4cc/0x11e0
>   audit_watch_handle_event+0x12c/0x1b0
>   send_to_group+0x5d0/0x8b0
>   fsnotify+0x615/0x28a0
>   fsnotify_move+0x1d8/0x630
>   vfs_rename+0xdcd/0x1df0
>   do_renameat2+0x9d4/0xbc0
>   __x64_sys_renameat+0x192/0x260
>   do_syscall_64+0x92/0x180
>   entry_SYSCALL_64_after_hwframe+0x76/0x7e
>  RIP: 0033:0x7f0491fe8c4e
>  Code: 0f 1f 40 00 48 8b 15 c1 e1 16 00 f7 d8 64 89 02 b8 ff ff ff ff
>  c3 66 0f 1f 44 00 00 f3 0f 1e fa 49 89 ca b8 08 01 00 00 0f 05 <48>
>  3d 00 f0 ff ff 77 0a c3 66 0f 1f 84 00 00 00 00 00 48 8b 15 89
>  RSP: 002b:00007ffc7210bf38 EFLAGS: 00000246 ORIG_RAX: 0000000000000108
>  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0491fe8c4e
>  RDX: 0000000000000003 RSI: 00007ffc7210e6c8 RDI: 00000000ffffff9c
>  RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
>  R10: 00005575eb2dae2a R11: 0000000000000246 R12: 00005575eb2dae2a
>  R13: 00007ffc7210e6c8 R14: 0000000000000003 R15: 00000000ffffff9c
>   </TASK>
> 
> The aforementioned deadlock can be consistently reproduced by running
> the script below:
> 
>  audit-dupe-exe-deadlock.sh
>  --------------------------
>  #!/bin/bash
>  auditctl -D
>  mkdir -p /tmp/foo
>  touch /tmp/file
>  auditctl -a always,exit -F exe=/tmp/file -F path=/tmp/file -S all -k dr
>  mv /tmp/file /tmp/foo/file
>  rm -Rf /tmp/foo
> 
> This patch fixes the issue by introducing struct audit_watch_ctx to pass
> the fsnotify event context down to audit_alloc_mark(). By utilizing the
> already-resolved directory inode provided by the event, we bypass the
> kern_path_parent() path resolution entirely, safely avoiding the
> recursive lock. Furthermore, it explicitly allows duplicate fsnotify
> marks (allow_dups = 1) during the rename update, allowing the new rule's
> mark to safely coexist with the old rule's mark until the old rule is
> freed.
> 
> ps.: this issue was identified and reproduced during a comprehensive
> code coverage analysis of the audit subsystem. The full report is
> available at the link below.
> 
> Fixes: 34d99af52ad4 ("audit: implement audit by executable")
> Link: https://people.redhat.com/rrobaina/audit-code-coverage-analysis.pdf
> Acked-by: Waiman Long <longman@redhat.com>
> Acked-by: Richard Guy Briggs <rgb@redhat.com>
> Signed-off-by: Ricardo Robaina <rrobaina@redhat.com>
> ---
> Changes in v2:
> - New patch order: now patch 2/2 (was 1/2 in v1) per maintainer feedback
> - Refactored audit_alloc_mark() to use local dir/child inode variables,
>   eliminating code duplication in the critical execution path
> - Unified fsnotify_add_inode_mark() call using allow_dups variable:
>   allow_dups=0 for manual rule additions (ctx==NULL, no duplicates allowed),
>   allow_dups=1 for fsnotify events (ctx!=NULL, temporary coexistence during
>   rename operations)
> 
>  kernel/audit.h          | 13 ++++++++++---
>  kernel/audit_fsnotify.c | 32 +++++++++++++++++++++++---------
>  kernel/audit_watch.c    | 25 +++++++++++++++++--------
>  kernel/auditfilter.c    |  9 +++++----
>  4 files changed, 55 insertions(+), 24 deletions(-)

Similar to patch 1/2, I want to give this some extra time in linux-next,
so I'm going to mark it for stable but merge it into audit/dev.

Regardless, good work here - thanks!

--
paul-moore.com