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

[Ricardo Robaina]

On Tue, Sep 22, 2026 at 5:34 PM Jérémy Jean
<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>

Looks good to me. I've checked that audit-testsuite passes cleanly.

Reviewed-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>
Tested-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>

# uname -r
7.3.0-rc4+

# make test
make -C tests test
Running as   user    root
        with context unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
        on   system  Fedora

amcast_joinpart/test ................. ok
backlog_wait_time_actual_reset/test .. ok
bpf/test ............................. ok
coredump/test ........................ ok
exec_execve/test ..................... ok
exec_name/test ....................... ok
fanotify/test ........................ ok
field_compare/test ................... ok
file_create/test ..................... ok
file_delete/test ..................... ok
file_permission/test ................. ok
file_rename/test ..................... ok
filter_device/test ................... ok
filter_exclude/test .................. ok
filter_exit/test ..................... ok
filter_inode/test .................... ok
filter_saddr_fam/test ................ ok
filter_sessionid/test ................ ok
io_uring/test ........................ ok
login_tty/test ....................... ok
lost_reset/test ...................... ok
netfilter_pkt/test ................... ok
signal/test .......................... ok
syscalls_file/test ................... ok
syscall_module/test .................. ok
syscall_socketcall/test .............. ok
time_change/test ..................... ok
user_msg/test ........................ ok
All tests successful.
Files=28, Tests=303, 69 wallclock secs ( 0.08 usr  0.03 sys + 36.64
cusr  1.87 csys = 38.62 CPU)
Result: PASS


> ---
>
> 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(-)
>
> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index 1ed19b775912..f2e81be8265e 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -545,22 +545,38 @@ static void kill_rules(struct audit_context *context, struct audit_tree *tree)
>  {
>         struct audit_krule *rule, *next;
>         struct audit_entry *entry;
> +       bool need_sync = false;
>
>         list_for_each_entry_safe(rule, next, &tree->rules, rlist) {
>                 entry = container_of(rule, struct audit_entry, rule);
>
> -               list_del_init(&rule->rlist);
>                 if (rule->tree) {
>                         /* not a half-baked one */
>                         audit_tree_log_remove_rule(context, rule);
> -                       if (entry->rule.exe)
> -                               audit_remove_mark(entry->rule.exe);
>                         rule->tree = NULL;
>                         list_del_rcu(&entry->list);
>                         list_del(&entry->rule.list);
> -                       call_rcu(&entry->rcu, audit_free_rule_rcu);
> +                       if (entry->rule.exe)
> +                               need_sync = true;
> +               } else {
> +                       list_del_init(&rule->rlist);
>                 }
>         }
> +
> +       if (list_empty(&tree->rules))
> +               return;
> +
> +       if (need_sync)
> +               synchronize_rcu();
> +
> +       list_for_each_entry_safe(rule, next, &tree->rules, rlist) {
> +               entry = container_of(rule, struct audit_entry, rule);
> +
> +               list_del_init(&rule->rlist);
> +               if (entry->rule.exe)
> +                       audit_remove_mark(entry->rule.exe);
> +               call_rcu(&entry->rcu, audit_free_rule_rcu);
> +       }
>  }
>
>  /*
>

--Ricardo