Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753513AbdFSTMD (ORCPT + 2 others); Mon, 19 Jun 2017 15:12:03 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:52319 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753408AbdFSSgi (ORCPT ); Mon, 19 Jun 2017 14:36:38 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: Eryu Guan , "Theodore Ts'o" , Jiri Slaby , Willy Tarreau Subject: [PATCH 3.10 006/268] ext4: validate s_first_meta_bg at mount time Date: Mon, 19 Jun 2017 20:28:25 +0200 Message-Id: <1497897167-14556-7-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1497897167-14556-1-git-send-email-w@1wt.eu> References: <1497897167-14556-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: From: Eryu Guan commit 3a4b77cd47bb837b8557595ec7425f281f2ca1fe upstream. Ralf Spenneberg reported that he hit a kernel crash when mounting a modified ext4 image. And it turns out that kernel crashed when calculating fs overhead (ext4_calculate_overhead()), this is because the image has very large s_first_meta_bg (debug code shows it's 842150400), and ext4 overruns the memory in count_overhead() when setting bitmap buffer, which is PAGE_SIZE. ext4_calculate_overhead(): buf = get_zeroed_page(GFP_NOFS); <=== PAGE_SIZE buffer blks = count_overhead(sb, i, buf); count_overhead(): for (j = ext4_bg_num_gdb(sb, grp); j > 0; j--) { <=== j = 842150400 ext4_set_bit(EXT4_B2C(sbi, s++), buf); <=== buffer overrun count++; } This can be reproduced easily for me by this script: #!/bin/bash rm -f fs.img mkdir -p /mnt/ext4 fallocate -l 16M fs.img mke2fs -t ext4 -O bigalloc,meta_bg,^resize_inode -F fs.img debugfs -w -R "ssv first_meta_bg 842150400" fs.img mount -o loop fs.img /mnt/ext4 Fix it by validating s_first_meta_bg first at mount time, and refusing to mount if its value exceeds the largest possible meta_bg number. [js] use EXT4_HAS_INCOMPAT_FEATURE instead of new ext4_has_feature_meta_bg Reported-by: Ralf Spenneberg Signed-off-by: Eryu Guan Signed-off-by: Theodore Ts'o Reviewed-by: Andreas Dilger Signed-off-by: Jiri Slaby Signed-off-by: Willy Tarreau --- fs/ext4/super.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index d609efd..b44dc28 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3777,6 +3777,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) (EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb))); db_count = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) / EXT4_DESC_PER_BLOCK(sb); + if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG)) { + if (le32_to_cpu(es->s_first_meta_bg) >= db_count) { + ext4_msg(sb, KERN_WARNING, + "first meta block group too large: %u " + "(group descriptor block count %u)", + le32_to_cpu(es->s_first_meta_bg), db_count); + goto failed_mount; + } + } sbi->s_group_desc = ext4_kvmalloc(db_count * sizeof(struct buffer_head *), GFP_KERNEL); -- 2.8.0.rc2.1.gbe9624a