From patchwork Thu Dec 1 08:18:28 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 9455567 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 8C19160585 for ; Thu, 1 Dec 2016 08:18:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7995B2849C for ; Thu, 1 Dec 2016 08:18:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6BAF7284A4; Thu, 1 Dec 2016 08:18:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D78F12849C for ; Thu, 1 Dec 2016 08:18:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757315AbcLAISw (ORCPT ); Thu, 1 Dec 2016 03:18:52 -0500 Received: from mx2.suse.de ([195.135.220.15]:35880 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757208AbcLAISv (ORCPT ); Thu, 1 Dec 2016 03:18:51 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C7419AABE; Thu, 1 Dec 2016 08:18:48 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 16E921E2FB0; Thu, 1 Dec 2016 09:18:47 +0100 (CET) From: Jan Kara To: Jens Axboe Cc: Andrew Morton , Wei Fang , linux-block@vger.kernel.org, Christoph Hellwig , Rabin Vincent , stable@vger.kernel.org, Jan Kara Subject: [PATCH] block: protect iterate_bdevs() against concurrent close Date: Thu, 1 Dec 2016 09:18:28 +0100 Message-Id: <1480580308-15342-1-git-send-email-jack@suse.cz> X-Mailer: git-send-email 2.6.6 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Rabin Vincent If a block device is closed while iterate_bdevs() is handling it, the following NULL pointer dereference occurs because bdev->b_disk is NULL in bdev_get_queue(), which is called from blk_get_backing_dev_info() (in turn called by the mapping_cap_writeback_dirty() call in __filemap_fdatawrite_range()): BUG: unable to handle kernel NULL pointer dereference at 0000000000000508 IP: [] blk_get_backing_dev_info+0x10/0x20 PGD 9e62067 PUD 9ee8067 PMD 0 Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC Modules linked in: CPU: 1 PID: 2422 Comm: sync Not tainted 4.5.0-rc7+ #400 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) task: ffff880009f4d700 ti: ffff880009f5c000 task.ti: ffff880009f5c000 RIP: 0010:[] [] blk_get_backing_dev_info+0x10/0x20 RSP: 0018:ffff880009f5fe68 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff88000ec17a38 RCX: ffffffff81a4e940 RDX: 7fffffffffffffff RSI: 0000000000000000 RDI: ffff88000ec176c0 RBP: ffff880009f5fe68 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: ffff88000ec17860 R13: ffffffff811b25c0 R14: ffff88000ec178e0 R15: ffff88000ec17a38 FS: 00007faee505d700(0000) GS:ffff88000fb00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000508 CR3: 0000000009e8a000 CR4: 00000000000006e0 Stack: ffff880009f5feb8 ffffffff8112e7f5 0000000000000000 7fffffffffffffff 0000000000000000 0000000000000000 7fffffffffffffff 0000000000000001 ffff88000ec178e0 ffff88000ec17860 ffff880009f5fec8 ffffffff8112e81f Call Trace: [] __filemap_fdatawrite_range+0x85/0x90 [] filemap_fdatawrite+0x1f/0x30 [] fdatawrite_one_bdev+0x16/0x20 [] iterate_bdevs+0xf2/0x130 [] sys_sync+0x63/0x90 [] entry_SYSCALL_64_fastpath+0x12/0x76 Code: 0f 1f 44 00 00 48 8b 87 f0 00 00 00 55 48 89 e5 <48> 8b 80 08 05 00 00 5d RIP [] blk_get_backing_dev_info+0x10/0x20 RSP CR2: 0000000000000508 ---[ end trace 2487336ceb3de62d ]--- The crash is easily reproducible by running the following command, if an msleep(100) is inserted before the call to func() in iterate_devs(): while :; do head -c1 /dev/nullb0; done > /dev/null & while :; do sync; done Fix it by holding the bd_mutex across the func() call and only calling func() if the bdev is opened. Cc: stable@vger.kernel.org Fixes: 5c0d6b60a0ba46d45020547eacf7199171920935 Reported-and-tested-by: Wei Fang Signed-off-by: Rabin Vincent Signed-off-by: Jan Kara Reviewed-by: Christoph Hellwig --- fs/block_dev.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 05b553368bb4..899fa8ccc347 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1950,6 +1950,7 @@ void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg) spin_lock(&blockdev_superblock->s_inode_list_lock); list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) { struct address_space *mapping = inode->i_mapping; + struct block_device *bdev; spin_lock(&inode->i_lock); if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW) || @@ -1970,8 +1971,12 @@ void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg) */ iput(old_inode); old_inode = inode; + bdev = I_BDEV(inode); - func(I_BDEV(inode), arg); + mutex_lock(&bdev->bd_mutex); + if (bdev->bd_openers) + func(bdev, arg); + mutex_unlock(&bdev->bd_mutex); spin_lock(&blockdev_superblock->s_inode_list_lock); }