This is a note to let you know that I've just added the patch titled f2fs: fix to invalidate dcc->f2fs_issue_discard in error path to the 5.15-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-to-invalidate-dcc-f2fs_issue_discard-in-err.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 941cb02e94e488b756179422a1b8f9e95ce4c606 Author: Chao Yu <chao@xxxxxxxxxx> Date: Fri Oct 21 10:34:22 2022 +0800 f2fs: fix to invalidate dcc->f2fs_issue_discard in error path [ 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@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-by: syzbot+729c925c2d9fc495ddee@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Chao Yu <chao@xxxxxxxxxx> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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; }