kernel/audit_tree.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-)
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@oss.cyber.gouv.fr>
---
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@oss.cyber.gouv.fr/
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);
+ }
}
/*
On Tue, Sep 22, 2026 at 5:34 PM Jérémy Jean
<Jeremy.Jean@oss.cyber.gouv.fr> 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@oss.cyber.gouv.fr>
Looks good to me. I've checked that audit-testsuite passes cleanly.
Reviewed-by: Ricardo Robaina <rrobaina@redhat.com>
Tested-by: Ricardo Robaina <rrobaina@redhat.com>
# 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@oss.cyber.gouv.fr/
>
> 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
On 22 September 2026 21:27:35 BST, "Jérémy Jean"
<Jeremy.Jean@oss.cyber.gouv.fr> 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
Reviewed-by: Bradley Morgan <brads@mainlining.org>
>Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
>---
>
>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@oss.cyber.gouv.fr/
>
> 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);
>+ }
> }
>
> /*
--- Thanks!
"I'm not a very positive person" - Linus torvalds
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