From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E73B26F30B for ; Sat, 27 Jul 2024 15:27:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722094023; cv=none; b=K/MmWwBTnYT+ZHo3HoFmkhARrcdH+Tz0hViHToM+7T7J6Wqv0RsmnaVETkmGqnk4vx5lK4KXLGX3Ivycq7zJUKPwwLEXfBEfC4IrYHXjaLdiDjuGEOlr5i7AhPhPme0YJAT76CS7H9dnOfSXSNSW55wq/Yt/BG5QYj20VZukeUU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722094023; c=relaxed/simple; bh=rcuyZk++ao7a339NuIqP/aH38I07fe8AieeU7rnNYhQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Gnut/pSr/uuiegU+zLUnKXMMBGZaHnS5MHTS7bINXDoA7Y8u791OEeDtKlg7wiqY58yhljWKXv8Lm8+m2hLQh3DLA3KUeh3ZmvoG2yURuUl1vq2jAeZNaRM2463pKwyxCyPGooAUF9kWr4j/ejpVZc1vaSAYPxm557n7qd9sfXA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jS+fgueU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jS+fgueU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F05DC32781; Sat, 27 Jul 2024 15:27:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722094022; bh=rcuyZk++ao7a339NuIqP/aH38I07fe8AieeU7rnNYhQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jS+fgueUdt9LXpCLv+BvHwMNLSYa7FVjEu/RT5JGX8MEPC47NR7z4uEhUsH80B3Hr cHbl64JkL2ipNIU6QRrD8tiHDTDH8sBhOW8gV38326GvoPqW9KBAuoNa4GQO3ho0fl 981Aq8uIamCH6bh5Vmt1qH1fj9O9ngTl9YdVx9F4dGsOUPDtFUYziHMg4UTcKhgUdv o5YKmwf/wJyLnO0mErf6EUs2C4xt2VvoD2dc7xa97xz9JR+A0T0TG06DHnGNIkpRk3 8evM7oVtpMbbvKp0XWf8Qbc1E60TDYJls47ya2bnjRaa01+J10L6akWBahoOPff/j7 Vlv3y8U52+ftA== Date: Sat, 27 Jul 2024 15:27:00 +0000 From: Jaegeuk Kim To: Chao Yu Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com Subject: Re: [PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread() Message-ID: References: <20240725020841.894814-1-chao@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On 07/27, Jaegeuk Kim wrote: > On 07/25, Chao Yu wrote: > > syzbot reports a f2fs bug as below: > > > > __dump_stack lib/dump_stack.c:88 [inline] > > dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 > > print_report+0xe8/0x550 mm/kasan/report.c:491 > > kasan_report+0x143/0x180 mm/kasan/report.c:601 > > kasan_check_range+0x282/0x290 mm/kasan/generic.c:189 > > instrument_atomic_read_write include/linux/instrumented.h:96 [inline] > > atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline] > > __refcount_add include/linux/refcount.h:184 [inline] > > __refcount_inc include/linux/refcount.h:241 [inline] > > refcount_inc include/linux/refcount.h:258 [inline] > > get_task_struct include/linux/sched/task.h:118 [inline] > > kthread_stop+0xca/0x630 kernel/kthread.c:704 > > f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210 > > f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283 > > f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline] > > __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325 > > vfs_ioctl fs/ioctl.c:51 [inline] > > __do_sys_ioctl fs/ioctl.c:907 [inline] > > __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893 > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > The root cause is below race condition, it may cause use-after-free > > issue in sbi->gc_th pointer. > > > > - remount > > - f2fs_remount > > - f2fs_stop_gc_thread > > - kfree(gc_th) > > - f2fs_ioc_shutdown > > - f2fs_do_shutdown > > - f2fs_stop_gc_thread > > - kthread_stop(gc_th->f2fs_gc_task) > > > > We will call f2fs_do_shutdown() in two paths: > > - for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore > > for fixing. > > - for f2fs_shutdown() path, it's safe since caller has already grabbed > > sb->s_umount semaphore. > > > > Reported-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com > > Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@google.com > > Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown") > > Signed-off-by: Chao Yu > > --- > > fs/f2fs/file.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c > > index 7a37f2b393b9..62d72da25754 100644 > > --- a/fs/f2fs/file.c > > +++ b/fs/f2fs/file.c > > @@ -2388,7 +2388,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg) > > } > > } > > > > + /* grab sb->s_umount to avoid racing w/ remount() */ > > + down_read(&sbi->sb->s_umount); > > Is this safe for freeze_bdev()? bdev_freeze -> fs_bdev_freeze -> get_bdev_super -> bdev_super_lock(bdev, true) -> super_lock(sb, true) -> __super_lock(sb, true) -> down_write(s_umount) > > > ret = f2fs_do_shutdown(sbi, in, readonly); > > + up_read(&sbi->sb->s_umount); > > > > if (need_drop) > > mnt_drop_write_file(filp); > > -- > > 2.40.1