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([2620:10d:c090:400::5:249c]) by smtp.gmail.com with ESMTPSA id t65sm3990442pfd.178.2020.02.13.12.20.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2020 12:20:46 -0800 (PST) Subject: Re: [PATCH] btrfs: Don't free tree_root when exiting btrfs_ioctl_get_subvol_info() To: Qu Wenruo , linux-btrfs@vger.kernel.org Cc: Marcos Paulo de Souza References: <20200213130157.39230-1-wqu@suse.com> From: Josef Bacik Message-ID: <2bca9e56-f5ce-6bf7-9e6f-8897f5c03d22@toxicpanda.com> Date: Thu, 13 Feb 2020 15:20:44 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200213130157.39230-1-wqu@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2/13/20 8:01 AM, 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 Ooops Reviewed-by: Josef Bacik Thanks, Josef