linux-ext4 - [patch 11/32] ext3, ext4: avoid divide by zero

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Date:	Mon, 17 Dec 2007 16:19:55 -0800
From:	akpm@...ux-foundation.org
To:	torvalds@...ux-foundation.org
Cc:	akpm@...ux-foundation.org, Andries.Brouwer@....nl, alan@...hat.com,
	linux-ext4@...r.kernel.org
Subject: [patch 11/32] ext3, ext4: avoid divide by zero

From: "Andries E. Brouwer" <Andries.Brouwer@....nl>

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: <linux-ext4@...r.kernel.org>
Acked-by: Alan Cox <alan@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 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)
_
-
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