From: akpm@linux-foundation.org Subject: [patch 11/32] ext3, ext4: avoid divide by zero Date: Mon, 17 Dec 2007 16:19:55 -0800 Message-ID: <200712180019.lBI0JuhJ009834@imap1.linux-foundation.org> Cc: akpm@linux-foundation.org, Andries.Brouwer@cwi.nl, alan@redhat.com, linux-ext4@vger.kernel.org To: torvalds@linux-foundation.org Return-path: Received: from smtp2.linux-foundation.org ([207.189.120.14]:44891 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753585AbXLRAUs (ORCPT ); Mon, 17 Dec 2007 19:20:48 -0500 Sender: linux-ext4-owner@vger.kernel.org List-ID: From: "Andries E. Brouwer" As it turns out, the kernel divides by EXT3_INODES_PER_GROUP(s) when mounting an ext3 filesystem. If that number is zero, a crash follows. Below a patch. This crash was reported by Joeri de Ruiter, Carst Tankink and Pim Vullers. Cc: Acked-by: Alan Cox Signed-off-by: Andrew Morton --- fs/ext3/super.c | 2 +- fs/ext4/super.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff -puN fs/ext3/super.c~ext3-ext4-avoid-divide-by-zero fs/ext3/super.c --- a/fs/ext3/super.c~ext3-ext4-avoid-divide-by-zero +++ a/fs/ext3/super.c @@ -1676,7 +1676,7 @@ static int ext3_fill_super (struct super sbi->s_blocks_per_group = le32_to_cpu(es->s_blocks_per_group); sbi->s_frags_per_group = le32_to_cpu(es->s_frags_per_group); sbi->s_inodes_per_group = le32_to_cpu(es->s_inodes_per_group); - if (EXT3_INODE_SIZE(sb) == 0) + if (EXT3_INODE_SIZE(sb) == 0 || EXT3_INODES_PER_GROUP(sb) == 0) goto cantfind_ext3; sbi->s_inodes_per_block = blocksize / EXT3_INODE_SIZE(sb); if (sbi->s_inodes_per_block == 0) diff -puN fs/ext4/super.c~ext3-ext4-avoid-divide-by-zero fs/ext4/super.c --- a/fs/ext4/super.c~ext3-ext4-avoid-divide-by-zero +++ a/fs/ext4/super.c @@ -1797,7 +1797,7 @@ static int ext4_fill_super (struct super sbi->s_desc_size = EXT4_MIN_DESC_SIZE; sbi->s_blocks_per_group = le32_to_cpu(es->s_blocks_per_group); sbi->s_inodes_per_group = le32_to_cpu(es->s_inodes_per_group); - if (EXT4_INODE_SIZE(sb) == 0) + if (EXT4_INODE_SIZE(sb) == 0 || EXT4_INODES_PER_GROUP(sb) == 0) goto cantfind_ext4; sbi->s_inodes_per_block = blocksize / EXT4_INODE_SIZE(sb); if (sbi->s_inodes_per_block == 0) _