[PATCH v3] audit: fix use-after-free in audit_add_watch
audit_add_watch stores locally krule->watch without taking a reference
on watch. Then, it calls audit_add_to_parent, and uses the watch stored
locally.
Unfortunately, it is possible that audit_add_to_parent updates
krule->watch.
When it happens, it also drops a reference of watch which
could free the watch.
How to reproduce (with KASAN enabled):
auditctl -w /etc/passwd -F success=0 -k test_passwd
auditctl -w /etc/passwd -F success=1 -k test_passwd2
The second call to auditctl triggers the use-after-free, because
audit_to_parent updates krule->watch to use a previous existing watch
and drops the reference to the newly created watch.
To fix the issue, we grab a reference of watch and we release it at the
end of the function.
Signed-off-by: Ronny Chevalier <ronny.chevalier(a)hp.com>
---
v3:
- Move audit_get_watch before audit_get_nd since it is using it
and call audit_put_watch if it fails.
v2:
- Move audit_get_watch before audit_find_parent. In the case of
audit_get_nd failing.
---
kernel/audit_watch.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index 6f249bdf2d84..787c7afdf829 100644
--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -420,6 +420,13 @@ int audit_add_watch(struct audit_krule *krule, struct list_head
**list)
struct path parent_path;
int h, ret = 0;
+ /*
+ * When we will be calling audit_add_to_parent, krule->watch might have
+ * been updated and watch might have been freed.
+ * So we need to keep a reference of watch.
+ */
+ audit_get_watch(watch);
+
mutex_unlock(&audit_filter_mutex);
/* Avoid calling path_lookup under audit_filter_mutex. */
@@ -428,8 +435,10 @@ int audit_add_watch(struct audit_krule *krule, struct list_head
**list)
/* caller expects mutex locked */
mutex_lock(&audit_filter_mutex);
- if (ret)
+ if (ret) {
+ audit_put_watch(watch);
return ret;
+ }
/* either find an old parent or attach a new one */
parent = audit_find_parent(d_backing_inode(parent_path.dentry));
@@ -447,6 +456,7 @@ int audit_add_watch(struct audit_krule *krule, struct list_head
**list)
*list = &audit_inode_hash[h];
error:
path_put(&parent_path);
+ audit_put_watch(watch);
return ret;
}
--
2.18.0