[PATCH 5.15 378/731] f2fs: fix to invalidate dcc->f2fs_issue_discard in error path

Greg Kroah-Hartman
2022-12-28T15:17:37Z

From: Chao Yu <chao@kernel.org>

[ Upstream commit 91586ce0d39a05f88795aa8814fb99b1387236b3 ]

Syzbot reports a NULL pointer dereference issue as below:

__refcount_add include/linux/refcount.h:193 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
get_task_struct include/linux/sched/task.h:110 [inline]
kthread_stop+0x34/0x1c0 kernel/kthread.c:703
f2fs_stop_discard_thread+0x3c/0x5c fs/f2fs/segment.c:1638
kill_f2fs_super+0x5c/0x194 fs/f2fs/super.c:4522
deactivate_locked_super+0x70/0xe8 fs/super.c:332
deactivate_super+0xd0/0xd4 fs/super.c:363
cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186
__cleanup_mnt+0x20/0x30 fs/namespace.c:1193
task_work_run+0xc4/0x14c kernel/task_work.c:177
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0x26c/0xbe0 kernel/exit.c:795
do_group_exit+0x60/0xe8 kernel/exit.c:925
__do_sys_exit_group kernel/exit.c:936 [inline]
__se_sys_exit_group kernel/exit.c:934 [inline]
__wake_up_parent+0x0/0x40 kernel/exit.c:934
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

The root cause of this issue is in error path of f2fs_start_discard_thread(),
it missed to invalidate dcc->f2fs_issue_discard, later kthread_stop() may
access invalid pointer.

Fixes: 4d67490498ac ("f2fs: Don't create discard thread when device doesn't support realtime discard")
Reported-by: syzbot+035a381ea1afb63f098d@syzkaller.appspotmail.com
Reported-by: syzbot+729c925c2d9fc495ddee@syzkaller.appspotmail.com
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/segment.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index af810b2d5d90..28939e3573ea 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2129,8 +2129,10 @@ int f2fs_start_discard_thread(struct f2fs_sb_info *sbi)

dcc->f2fs_issue_discard = kthread_run(issue_discard_thread, sbi,
"f2fs_discard-%u:%u", MAJOR(dev), MINOR(dev));
- if (IS_ERR(dcc->f2fs_issue_discard))
+ if (IS_ERR(dcc->f2fs_issue_discard)) {
err = PTR_ERR(dcc->f2fs_issue_discard);
+ dcc->f2fs_issue_discard = NULL;
+ }

return err;
}
--
2.35.1