This is a note to let you know that I've just added the patch titled f2fs: wait for sysfs kobject removal before freeing f2fs_sb_info to the 5.4-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-wait-for-sysfs-kobject-removal-before-freeing-f.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit fef39b35ac609a2cfddaee940ee231e8559dcd72 Author: Jamie Iles <jamie@xxxxxxxxxxxx> Date: Mon Oct 12 14:09:48 2020 +0100 f2fs: wait for sysfs kobject removal before freeing f2fs_sb_info [ Upstream commit ae284d87abade58c8db7760c808f311ef1ce693c ] syzkaller found that with CONFIG_DEBUG_KOBJECT_RELEASE=y, unmounting an f2fs filesystem could result in the following splat: kobject: 'loop5' ((____ptrval____)): kobject_release, parent 0000000000000000 (delayed 250) kobject: 'f2fs_xattr_entry-7:5' ((____ptrval____)): kobject_release, parent 0000000000000000 (delayed 750) ------------[ cut here ]------------ ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x98 WARNING: CPU: 0 PID: 699 at lib/debugobjects.c:485 debug_print_object+0x180/0x240 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 699 Comm: syz-executor.5 Tainted: G S 5.9.0-rc8+ #101 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x4d8 show_stack+0x34/0x48 dump_stack+0x174/0x1f8 panic+0x360/0x7a0 __warn+0x244/0x2ec report_bug+0x240/0x398 bug_handler+0x50/0xc0 call_break_hook+0x160/0x1d8 brk_handler+0x30/0xc0 do_debug_exception+0x184/0x340 el1_dbg+0x48/0xb0 el1_sync_handler+0x170/0x1c8 el1_sync+0x80/0x100 debug_print_object+0x180/0x240 debug_check_no_obj_freed+0x200/0x430 slab_free_freelist_hook+0x190/0x210 kfree+0x13c/0x460 f2fs_put_super+0x624/0xa58 generic_shutdown_super+0x120/0x300 kill_block_super+0x94/0xf8 kill_f2fs_super+0x244/0x308 deactivate_locked_super+0x104/0x150 deactivate_super+0x118/0x148 cleanup_mnt+0x27c/0x3c0 __cleanup_mnt+0x28/0x38 task_work_run+0x10c/0x248 do_notify_resume+0x9d4/0x1188 work_pending+0x8/0x34c Like the error handling for f2fs_register_sysfs(), we need to wait for the kobject to be destroyed before returning to prevent a potential use-after-free. Fixes: bf9e697ecd42 ("f2fs: expose features to sysfs entry") Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Cc: Chao Yu <chao@xxxxxxxxxx> Signed-off-by: Jamie Iles <jamie@xxxxxxxxxxxx> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c index 170934430d7d7..029e693e201cf 100644 --- a/fs/f2fs/sysfs.c +++ b/fs/f2fs/sysfs.c @@ -788,4 +788,5 @@ void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi) } kobject_del(&sbi->s_kobj); kobject_put(&sbi->s_kobj); + wait_for_completion(&sbi->s_kobj_unregister); }