6.6-stable review patch. If anyone has any objections, please let me know.
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From: Long Li leo.lilong@huawei.com
[ 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@huawei.com Reviewed-by: Chao Yu chao@kernel.org Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/f2fs/file.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
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: