From 1ab19c5de4c537ec0d9b21020395a5b5a6c059b2 Mon Sep 17 00:00:00 2001
From: Hillf Danton <hdanton@sina.com>
Date: Tue, 18 May 2021 16:46:25 +0800
Subject: [PATCH] gfs2: Fix use-after-free in gfs2_glock_shrink_scan
Git-commit: 1ab19c5de4c537ec0d9b21020395a5b5a6c059b2
Patch-mainline: v5.13-rc5
References: git-fixes
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>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>
---
fs/gfs2/glock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1351,6 +1351,7 @@ __acquires(&lru_lock)
while(!list_empty(list)) {
gl = list_entry(list->next, 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);
@@ -1397,7 +1398,6 @@ 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;
}