Re: [PATCH v2] audit: fix exe mark UAF in kill_rules()

[Paul Moore]

On Sep 22, 2026 =?UTF-8?q?J=C3=A9r=C3=A9my=20Jean?= <Jeremy.Jean@xxxxxxxxxxxxxxxxx> wrote:
> 
> kill_rules() removes mixed AUDIT_DIR and AUDIT_EXE rules when an audit
> tree is pruned. It drops entry->rule.exe before removing the rule from
> the RCU-visible filter lists.
> 
> After a rule has been installed with AUDIT_ADD_RULE, which requires
> CAP_AUDIT_CONTROL, removing the watched directory can race with another
> task that is still evaluating the rule. In that case, fsnotify can free
> the executable mark before the reader reaches audit_mark_compare(),
> causing a use-after-free.
> 
> KASAN reports:
> 
>     BUG: KASAN: slab-use-after-free in audit_mark_compare+0x8d/0xa0
> 
> Unlink the published rules from the RCU-visible lists and retain them
> on tree->rules for cleanup. If any rule has an executable mark, wait for
> a single RCU grace period before removing the marks and scheduling the
> entries for freeing. Otherwise, call_rcu() already provides the required
> deferred freeing without a synchronous wait.
> 
> Fixes: 34d99af52ad4 ("audit: implement audit by executable")
> Assisted-by: Codex:gpt-5
> Signed-off-by: Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>
> Tested-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>
> Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
> ---
> v2: Address Sashiko's review with Ricardo Robaina's improved patch:
> - Batch executable-mark teardown behind one synchronize_rcu() after
>   unlinking all rules, instead of waiting once per rule under the audit
>   mutexes.
> - Skip the synchronous wait when none of the removed rules has an
>   executable mark.
> 
> v1: https://lore.kernel.org/all/20260921195921.4174830-2-Jeremy.Jean@xxxxxxxxxxxxxxxxx/
> 
>  kernel/audit_tree.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)

Merged into audit/stable-7.3 with a stable tag, I'll send this up to Linus
next week after it has had some time in linux-next.  Thanks!

--
paul-moore.com