f2fs: wait for sysfs kobject removal before freeing f2fs_sb_info

Jamie Iles · gregkh · commit 1ad93f42c484 · 2020-10-29T10:08:02.000+01:00
[ Upstream commit ae284d8 ] 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+ hardkernel#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: bf9e697 ("f2fs: expose features to sysfs entry") Cc: Jaegeuk Kim <jaegeuk@kernel.org> Cc: Chao Yu <chao@kernel.org> Signed-off-by: Jamie Iles <jamie@nuviainc.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
@@ -964,4 +964,5 @@ 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);
 }

Original file line number	Diff line number	Diff line change
`@@ -964,4 +964,5 @@ void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi)`
`964`	`964`	`}`
`965`	`965`	`kobject_del(&sbi->s_kobj);`
`966`	`966`	`kobject_put(&sbi->s_kobj);`
	`967`	`+ wait_for_completion(&sbi->s_kobj_unregister);`
`967`	`968`	`}`