From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E13C2C43603 for ; Wed, 11 Dec 2019 05:00:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C1C7520836 for ; Wed, 11 Dec 2019 05:00:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726368AbfLKFAN (ORCPT ); Wed, 11 Dec 2019 00:00:13 -0500 Received: from mx2.suse.de ([195.135.220.15]:45508 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725768AbfLKFAN (ORCPT ); Wed, 11 Dec 2019 00:00:13 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0EA73AE07; Wed, 11 Dec 2019 05:00:12 +0000 (UTC) From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Zygo Blaxell Subject: [PATCH 1/3] btrfs: relocation: Fix a KASAN use-after-free bug due to extended reloc tree lifespan Date: Wed, 11 Dec 2019 13:00:02 +0800 Message-Id: <20191211050004.18414-2-wqu@suse.com> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191211050004.18414-1-wqu@suse.com> References: <20191211050004.18414-1-wqu@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org [BUG] When running a workload with balance start/cancel, snapshot creation and deletion, and fsstress, we can get the following KASAN report: ================================================================== BUG: KASAN: use-after-free in should_ignore_root+0x54/0xb0 [btrfs] Read of size 8 at addr ffff888146e340f0 by task btrfs/1216 CPU: 6 PID: 1216 Comm: btrfs Tainted: G O 5.5.0-rc1-custom+ #40 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack+0xc2/0x11a print_address_description.constprop.0+0x20/0x210 __kasan_report.cold+0x1b/0x41 kasan_report+0x12/0x20 check_memory_region+0x13c/0x1b0 __asan_loadN+0xf/0x20 should_ignore_root+0x54/0xb0 [btrfs] build_backref_tree+0x11af/0x2280 [btrfs] relocate_tree_blocks+0x391/0xb80 [btrfs] relocate_block_group+0x3e5/0xa00 [btrfs] btrfs_relocate_block_group+0x240/0x4d0 [btrfs] btrfs_relocate_chunk+0x53/0xf0 [btrfs] btrfs_balance+0xc91/0x1840 [btrfs] btrfs_ioctl_balance+0x416/0x4e0 [btrfs] btrfs_ioctl+0x8af/0x3e60 [btrfs] do_vfs_ioctl+0x831/0xb10 ksys_ioctl+0x67/0x90 __x64_sys_ioctl+0x43/0x50 do_syscall_64+0x79/0xe0 entry_SYSCALL_64_after_hwframe+0x49/0xbe [CAUSE] When should_ignore_root() accessing root->reloc_root, the reloc_root can be being dropped, thus root->reloc_root can be unreliable. [FIX] Check DEAD_RELOC_ROOT bit before accessing root->reloc_root. Furthermore in the context of should_ignore_root(), if the root has already gone through tree merge, we don't need to trace that root anymore. Thus we need to return 1, for root with dead reloc root. Reported-by: Zygo Blaxell Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots") Signed-off-by: Qu Wenruo --- fs/btrfs/relocation.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index d897a8e5e430..bb41b981e493 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -525,6 +525,10 @@ static int should_ignore_root(struct btrfs_root *root) if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state)) return 0; + /* This root has been merged with its reloc tree, so we can ignore it */ + if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state)) + return 1; + reloc_root = root->reloc_root; if (!reloc_root) return 0; -- 2.24.0