Commit 1ab19c5d authored May 18, 2021 by Hillf Danton Committed by Andreas Gruenbacher May 31, 2021

gfs2: Fix use-after-free in gfs2_glock_shrink_scan

The GLF_LRU flag is checked under lru_lock in gfs2_glock_remove_from_lru() to
remove the glock from the lru list in __gfs2_glock_put().

On the shrink scan path, the same flag is cleared under lru_lock but because
of cond_resched_lock(&lru_lock) in gfs2_dispose_glock_lru(), progress on the
put side can be made without deleting the glock from the lru list.

Keep GLF_LRU across the race window opened by cond_resched_lock(&lru_lock) to
ensure correct behavior on both sides - clear GLF_LRU after list_del under
lru_lock.

Reported-by: syzbot <syzbot+34ba7ddbf3021981a228@syzkaller.appspotmail.com>
Signed-off-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

parent b7f55d92

fs/gfs2/glock.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1795,6 +1795,7 @@ __acquires(&lru_lock)
		while(!list_empty(list)) {
		gl = list_first_entry(list, struct gfs2_glock, gl_lru);
		list_del_init(&gl->gl_lru);
		clear_bit(GLF_LRU, &gl->gl_flags);
		if (!spin_trylock(&gl->gl_lockref.lock)) {
		add_back_to_lru:
		list_add(&gl->gl_lru, &lru_list);
		@@ -1840,7 +1841,6 @@ static long gfs2_scan_glock_lru(int nr)
		if (!test_bit(GLF_LOCK, &gl->gl_flags)) {
		list_move(&gl->gl_lru, &dispose);
		atomic_dec(&lru_count);
		clear_bit(GLF_LRU, &gl->gl_flags);
		freed++;
		continue;
		}