This is a note to let you know that I've just added the patch titled
f2fs: fix race in concurrent f2fs_stop_gc_thread
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
f2fs-fix-race-in-concurrent-f2fs_stop_gc_thread.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit c70fb02a4614a97f90b89d77093cb9ebd41e8236
Author: Long Li <leo.lilong@xxxxxxxxxx>
Date: Mon Nov 4 10:05:42 2024 +0800
f2fs: fix race in concurrent f2fs_stop_gc_thread
[ Upstream commit 7b0033dbc48340a1c1c3f12448ba17d6587ca092 ]
In my test case, concurrent calls to f2fs shutdown report the following
stack trace:
Oops: general protection fault, probably for non-canonical address 0xc6cfff63bb5513fc: 0000 [#1] PREEMPT SMP PTI
CPU: 0 UID: 0 PID: 678 Comm: f2fs_rep_shutdo Not tainted 6.12.0-rc5-next-20241029-g6fb2fa9805c5-dirty #85
Call Trace:
<TASK>
? show_regs+0x8b/0xa0
? __die_body+0x26/0xa0
? die_addr+0x54/0x90
? exc_general_protection+0x24b/0x5c0
? asm_exc_general_protection+0x26/0x30
? kthread_stop+0x46/0x390
f2fs_stop_gc_thread+0x6c/0x110
f2fs_do_shutdown+0x309/0x3a0
f2fs_ioc_shutdown+0x150/0x1c0
__f2fs_ioctl+0xffd/0x2ac0
f2fs_ioctl+0x76/0xe0
vfs_ioctl+0x23/0x60
__x64_sys_ioctl+0xce/0xf0
x64_sys_call+0x2b1b/0x4540
do_syscall_64+0xa7/0x240
entry_SYSCALL_64_after_hwframe+0x76/0x7e
The root cause is a race condition in f2fs_stop_gc_thread() called from
different f2fs shutdown paths:
[CPU0] [CPU1]
---------------------- -----------------------
f2fs_stop_gc_thread f2fs_stop_gc_thread
gc_th = sbi->gc_thread
gc_th = sbi->gc_thread
kfree(gc_th)
sbi->gc_thread = NULL
< gc_th != NULL >
kthread_stop(gc_th->f2fs_gc_task) //UAF
The commit c7f114d864ac ("f2fs: fix to avoid use-after-free in
f2fs_stop_gc_thread()") attempted to fix this issue by using a read
semaphore to prevent races between shutdown and remount threads, but
it fails to prevent all race conditions.
Fix it by converting to write lock of s_umount in f2fs_do_shutdown().
Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
Signed-off-by: Long Li <leo.lilong@xxxxxxxxxx>
Reviewed-by: Chao Yu <chao@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ad26733f1f46c..c6bc4cbd72b9d 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2308,9 +2308,12 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
if (readonly)
goto out;
- /* grab sb->s_umount to avoid racing w/ remount() */
+ /*
+ * grab sb->s_umount to avoid racing w/ remount() and other shutdown
+ * paths.
+ */
if (need_lock)
- down_read(&sbi->sb->s_umount);
+ down_write(&sbi->sb->s_umount);
f2fs_stop_gc_thread(sbi);
f2fs_stop_discard_thread(sbi);
@@ -2319,7 +2322,7 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
clear_opt(sbi, DISCARD);
if (need_lock)
- up_read(&sbi->sb->s_umount);
+ up_write(&sbi->sb->s_umount);
f2fs_update_time(sbi, REQ_TIME);
out:
