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gfs2: Fix use-after-free in gfs2_glock_shrink_scan 

[ Upstream commit 1ab19c5de4c537ec0d9b21020395a5b5a6c059b2 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
pull/379/head^2
Hillf Danton 2021-05-18 16:46:25 +08:00 committed by Greg Kroah-Hartman
parent bb73f2f789
commit a61156314b
1 changed files with 1 additions and 1 deletions
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2
fs/gfs2/glock.c
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@ -1784,6 +1784,7 @@ __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);
@ -1829,7 +1830,6 @@ 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;
}