Commit 75845c6c authored by David Howells's avatar David Howells Committed by Jarkko Sakkinen
Browse files

keys: Fix UAF in key_put() 



Once a key's reference count has been reduced to 0, the garbage collector
thread may destroy it at any time and so key_put() is not allowed to touch
the key after that point.  The most key_put() is normally allowed to do is
to touch key_gc_work as that's a static global variable.

However, in an effort to speed up the reclamation of quota, this is now
done in key_put() once the key's usage is reduced to 0 - but now the code
is looking at the key after the deadline, which is forbidden.

Fix this by using a flag to indicate that a key can be gc'd now rather than
looking at the key's refcount in the garbage collector.

Fixes: 9578e327 ("keys: update key quotas in key_put()")
Reported-by: default avatar <syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/673b6aec.050a0220.87769.004a.GAE@google.com/


Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Tested-by: default avatar <syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
parent 88d324e6

include/linux/key.h

+1 −0
Original line number Diff line number Diff line
@@ -236,6 +236,7 @@ struct key { 
#define KEY_FLAG_ROOT_CAN_INVAL	7	/* set if key can be invalidated by root without permission */

#define KEY_FLAG_KEEP		8	/* set if key should not be removed */

#define KEY_FLAG_UID_KEYRING	9	/* set if key is a user or user session keyring */

#define KEY_FLAG_FINAL_PUT	10	/* set if final put has happened on key */



	/* the key type and key description string

	 * - the desc is used to match a key against search criteria

security/keys/gc.c

+3 −1
Original line number Diff line number Diff line
@@ -218,8 +218,10 @@ static void key_garbage_collector(struct work_struct *work) 
		key = rb_entry(cursor, struct key, serial_node);

		cursor = rb_next(cursor);



		if (refcount_read(&key->usage) == 0)

		if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) {

			smp_mb(); /* Clobber key->user after FINAL_PUT seen. */

			goto found_unreferenced_key;

		}



		if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {

			if (key->type == key_gc_dead_keytype) {

security/keys/key.c

+2 −0
Original line number Diff line number Diff line
@@ -658,6 +658,8 @@ void key_put(struct key *key) 
				key->user->qnbytes -= key->quotalen;

				spin_unlock_irqrestore(&key->user->lock, flags);

			}

			smp_mb(); /* key->user before FINAL_PUT set. */

			set_bit(KEY_FLAG_FINAL_PUT, &key->flags);

			schedule_work(&key_gc_work);

		}

	}