From nobody Mon Feb 9 00:25:45 2026 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 76A5B6AB9 for ; Thu, 25 Jul 2024 02:08:49 +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=1721873329; cv=none; b=l4YkpK089xgdqYnaw9EkbrNcyJ0JLZBN1cWTC4K7YG2v2H+YJaDvuv4d7br61QbrjYMIgdccIEj1H0lxm+INJaP8t4+RAM37jVyhjnvWXE4g8ZHUUi1WF7G2GRCDiMU/1Kl6OvAWXX99Odu61tXkNiUPR4OGSOCxK6fM/xzxoCI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721873329; c=relaxed/simple; bh=hZLfXkRQOcL/yljHe3PrGXlzhVc26RzCNlLV2gPi8CA=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=elNeyqyp4hFcCKBmhQIp+mih5FUbd7P7WQIk/lNXAtKLUdBpiK9Q+Y84kn2RdUurzc8B0W/axxA9X5draxXcrhgTfZMSYIyC7HpRv0edmGMEOHNEDiZabzQdKkksrvfAtnd6uIx6RHZ6DKNN/XzDcYA7yWMFQxVNMkkqLhie5vw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tBdWxGzL; 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="tBdWxGzL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5B3DC32781; Thu, 25 Jul 2024 02:08:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721873329; bh=hZLfXkRQOcL/yljHe3PrGXlzhVc26RzCNlLV2gPi8CA=; h=From:To:Cc:Subject:Date:From; b=tBdWxGzL64Mr4pUx0gjhtN2hihht0CzcvZAbXYcmuyKIOmABqQtf8NHMmhsOBmEYL O57J+vcsbbHfCjehLl1Nlx4GY9YFY5IrwtSDbu9eVS16NCZqOlfmFDi5dXMD7lB8i5 R8yfrC45eZ56RbhjuC+PT+EeYOqtc8KfUfu2mYFfKDeVUzzJ6hVAyKufcCvLlmCmmJ hborJvsHX1RGNDK3Bze+VLFLyLGEAkb3Q/0vU8kxXzqy5P1VCwAwN4Wdp0p+PgfpUJ 3kusAWvIpvZJcHd2bxf5uKz3iwXg9+to6tMdzmJkf6PGDW6yERvYycazFnr/OwJR60 b6ApY+wjJeB3w== From: Chao Yu To: jaegeuk@kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, Chao Yu , syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com Subject: [PATCH] f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread() Date: Thu, 25 Jul 2024 10:08:41 +0800 Message-Id: <20240725020841.894814-1-chao@kernel.org> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 [i= nline] __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/0000000000005c7ccb061e032b= 9b@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, unsi= gned long arg) } } =20 + /* grab sb->s_umount to avoid racing w/ remount() */ + down_read(&sbi->sb->s_umount); ret =3D f2fs_do_shutdown(sbi, in, readonly); + up_read(&sbi->sb->s_umount); =20 if (need_drop) mnt_drop_write_file(filp); --=20 2.40.1