From patchwork Wed Nov 9 09:50:18 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liu Shixin X-Patchwork-Id: 13037267 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0B90C433FE for ; Wed, 9 Nov 2022 09:02:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230235AbiKIJCq (ORCPT ); Wed, 9 Nov 2022 04:02:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39342 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230237AbiKIJCe (ORCPT ); Wed, 9 Nov 2022 04:02:34 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 205831F9E5; Wed, 9 Nov 2022 01:02:31 -0800 (PST) Received: from dggpemm500024.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4N6f9S5GrjzHvfB; Wed, 9 Nov 2022 17:02:04 +0800 (CST) Received: from dggpemm100009.china.huawei.com (7.185.36.113) by dggpemm500024.china.huawei.com (7.185.36.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 9 Nov 2022 17:02:29 +0800 Received: from huawei.com (10.175.113.32) by dggpemm100009.china.huawei.com (7.185.36.113) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 9 Nov 2022 17:02:28 +0800 From: Liu Shixin To: Alexander Viro CC: , , "Liu Shixin" Subject: [PATCH] fs/buffer: fix a NULL pointer dereference in drop_buffers() Date: Wed, 9 Nov 2022 17:50:18 +0800 Message-ID: <20221109095018.4108726-1-liushixin2@huawei.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Originating-IP: [10.175.113.32] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm100009.china.huawei.com (7.185.36.113) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org syzbot found a null-ptr-deref by KASAN: BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline] BUG: KASAN: null-ptr-deref in atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline] BUG: KASAN: null-ptr-deref in buffer_busy fs/buffer.c:2856 [inline] BUG: KASAN: null-ptr-deref in drop_buffers+0x61/0x2f0 fs/buffer.c:2868 Read of size 4 at addr 0000000000000060 by task syz-executor.5/24786 CPU: 0 PID: 24786 Comm: syz-executor.5 Not tainted 6.0.0-syzkaller-09589-g55be6084c8e0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106 print_report+0xf1/0x220 mm/kasan/report.c:436 kasan_report+0xfb/0x130 mm/kasan/report.c:495 kasan_check_range+0x2a7/0x2e0 mm/kasan/generic.c:189 instrument_atomic_read include/linux/instrumented.h:71 [inline] atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline] buffer_busy fs/buffer.c:2856 [inline] drop_buffers+0x61/0x2f0 fs/buffer.c:2868 try_to_free_buffers+0x2b1/0x640 fs/buffer.c:2898 [...] We use folio_has_private() to decide whether call filemap_release_folio(), which may call try_to_free_buffers() then. folio_has_private() return true for both PG_private and PG_private_2. We should only call try_to_free_buffers() for case PG_private. So we should recheck PG_private in try_to_free_buffers(). Reported-by: syzbot+fbdb4ec578ebdcfb9ed2@syzkaller.appspotmail.com Fixes: 266cf658efcf ("FS-Cache: Recruit a page flags for cache management") Signed-off-by: Liu Shixin --- fs/buffer.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/buffer.c b/fs/buffer.c index d9c6d1fbb6dd..c302b578e437 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2822,6 +2822,9 @@ bool try_to_free_buffers(struct folio *folio) if (folio_test_writeback(folio)) return false; + if (!folio_test_private(folio)) + return false; + if (mapping == NULL) { /* can this still happen? */ ret = drop_buffers(folio, &buffers_to_free); goto out;