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 DB3AA17F4EC for ; Sat, 27 Jul 2024 15:11:21 +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=1722093081; cv=none; b=Y1TrVVkEWTbN/0HH86sIyBf+XjhtcqXU35ozLEzw6Z3UkygetuuuyhzoWYEQKpp4o+/krVvOz4w3Xms+Qu61ltmGOxgTSp9ise4hXKu3ilz2yeR4oWZ7daoi3qEtdPm5gDXP+kTA3GNu3lX1Wlt9lOvq9MZ0QJhb7FJcr/LCpho= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722093081; c=relaxed/simple; bh=cwAkkMmbUKCcFkt3RabHqDWW3gTFHRVL4u2/cL+hQHQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uDrBduRI4NACISB7E2RvbnHlL/VkaMY9X7Oi9Oq9sWCf946dgUYz4mGaQYY0N4WmkLiiXOahw/KoF0aB1EY5yk2vve4hLe/thV066QSqQcgNIt58BALHKXzu6JM9/tL5nD5kjfsYGeVAhi6vNBAdAW58r4amEY48uXZlDj4T03U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KvTOtMqz; 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="KvTOtMqz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86A0DC32781; Sat, 27 Jul 2024 15:11:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722093081; bh=cwAkkMmbUKCcFkt3RabHqDWW3gTFHRVL4u2/cL+hQHQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KvTOtMqzOr+iWbBD4YNWxLZutjs7om88GyAzMyjJ6dI/0U4AglLeierRh+25Yms5j RUFL94O+9SsRs5uY8Z/2Tlgd9B+iUP9JFWalPtt5iBKsAn5zjwbVayqpB7K60+Fnxc Hzm87TSEn3X4UHnh27rCVIYNu/oft12GUE0LywbIYQcHnEoSanv7wg1ZM4rUxE4n9t BloNeFRhZMpR9bKMjzcs6J3oTVW81Yc57Pq2n5lsEPD1VuvUVWSWV7Y7abDASpZkuo 0FQe42Ioshl4vg9CBwQ4axB4LFbTsMLxbH3NJrWAr+iOTME2h0qeW0WJu+lvxjCqmr 7p0tBpajiQdQg== Date: Sat, 27 Jul 2024 15:11:19 +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: <20240725020841.894814-1-chao@kernel.org> 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()? > ret = f2fs_do_shutdown(sbi, in, readonly); > + up_read(&sbi->sb->s_umount); > > if (need_drop) > mnt_drop_write_file(filp); > -- > 2.40.1