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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 5FCCAC2BA83 for ; Thu, 13 Feb 2020 17:40:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 418FF218AC for ; Thu, 13 Feb 2020 17:40:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727609AbgBMRkf (ORCPT ); Thu, 13 Feb 2020 12:40:35 -0500 Received: from mx2.suse.de ([195.135.220.15]:57516 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726780AbgBMRkf (ORCPT ); Thu, 13 Feb 2020 12:40:35 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id A77EFAD3B; Thu, 13 Feb 2020 17:40:33 +0000 (UTC) Message-ID: Subject: Re: [PATCH] btrfs: Don't free tree_root when exiting btrfs_ioctl_get_subvol_info() From: Marcos Paulo de Souza To: Qu Wenruo , linux-btrfs@vger.kernel.org Date: Thu, 13 Feb 2020 14:43:32 -0300 In-Reply-To: <20200213130157.39230-1-wqu@suse.com> References: <20200213130157.39230-1-wqu@suse.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, 2020-02-13 at 21:01 +0800, Qu Wenruo wrote: > [BUG] > When calling BTRF_IOC_GET_SUBVOL_INFO ioctl, we can easily hit the > following backtrace: > BUG: kernel NULL pointer dereference, address: 0000000000000024 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: 0000 [#1] SMP PTI > CPU: 0 PID: 27421 Comm: python3 Not tainted 5.6.0-rc1+ #539 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel- > 1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 > RIP: 0010:btrfs_root_node+0x7/0x30 [btrfs] > Call Trace: > btrfs_read_lock_root_node+0x1f/0x40 [btrfs] > btrfs_search_slot+0x60f/0xa40 [btrfs] > btrfs_ioctl+0x11f7/0x30b0 [btrfs] > ksys_ioctl+0x82/0xc0 > __x64_sys_ioctl+0x11/0x20 > do_syscall_64+0x43/0x130 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x7fcb78d43387 > ---[ end trace 1c21a7c6c0523b8c ]--- > > [CAUSE] > We're abusing local @root, it's originally a subvolume root, but in > root backref search, it's re-assigned to tree_root. > > Then we call "btrfs_put_root(root);" when exiting. > If that @root is reassgined to tree-root, we freed the most important > tree, and cause use-after-free. > > [FIX] > Don't re-assgiend @root, use fs_info->tree_root directly. > > Reported-by: Marcos Paulo de Souza > Fixes: 8c319b625e0a ("btrfs: hold a ref on the root in > btrfs_ioctl_get_subvol_info") > [To David: please fold the fix into that commit] > Signed-off-by: Qu Wenruo This patch fixed the issue, thanks Qu. Tested-by: Marcos Paulo de Souza > --- > fs/btrfs/ioctl.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c > index e6b7cf45a066..43195970f70c 100644 > --- a/fs/btrfs/ioctl.c > +++ b/fs/btrfs/ioctl.c > @@ -2696,17 +2696,16 @@ static int btrfs_ioctl_get_subvol_info(struct > file *file, void __user *argp) > subvol_info->rtime.nsec = btrfs_stack_timespec_nsec(&root_item- > >rtime); > > if (key.objectid != BTRFS_FS_TREE_OBJECTID) { > - /* Search root tree for ROOT_BACKREF of this subvolume > */ > - root = fs_info->tree_root; > - > key.type = BTRFS_ROOT_BACKREF_KEY; > key.offset = 0; > - ret = btrfs_search_slot(NULL, root, &key, path, 0, 0); > + > + /* Search root tree for ROOT_BACKREF of this subvolume > */ > + ret = btrfs_search_slot(NULL, fs_info->tree_root, &key, > path, 0, 0); > if (ret < 0) { > goto out; > } else if (path->slots[0] >= > btrfs_header_nritems(path->nodes[0])) { > - ret = btrfs_next_leaf(root, path); > + ret = btrfs_next_leaf(fs_info->tree_root, > path); > if (ret < 0) { > goto out; > } else if (ret > 0) {