Re: [Bugme-new] [Bug 11266] New: unable to handle kernel paging request in ext2_free_blocks

Jan Kara
2008-08-18T14:58:42Z

> On Thu, Aug 07, 2008 at 11:07:17PM +0300, Sami Liedes wrote:
> > On Thu, Aug 07, 2008 at 10:52:51AM -0700, Andrew Morton wrote:
> > > Yes, please do test 2.6.26.
> >
> > Did that. I can reproduce the same crash on 2.6.26 and 2.6.26.2.
>
> 2.6.25.15 crashes too, so I might have been wrong about 2.6.25.4
> working (unless something changed between those two versions).
I think this is the same problem Vegard reported in
http://marc.info/?l=linux-ext4&m=121637999611618&w=2.
The problem seems to be in ext2_valid_block_bitmap() which does

bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
offset = bitmap_blk - group_first_block;
if (!ext2_test_bit(offset, bh->b_data))

(and similarly for inode bitmap). Now when the group descriptor is
corrupted, this simply accesses beyond the bh->b_data...
The patch below should hopefully fix the issue. Can you test it
please?

Honza
--
Jan Kara <jack@suse.cz>
SuSE CR Labs
---

>From 06953717138efe3ad535e78343beb7204ac0d274 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Mon, 18 Aug 2008 16:45:11 +0200
Subject: [PATCH] ext2: Check for corrupted group descriptor before using data in it

We have to check whether a group descriptor isn't corrupted in
read_block_bitmap(). Otherwise ext2_valid_block_bitmap() will try
to access bits outside of bitmap and Oops happens.

CC: Vegard Nossum <vegard.nossum@gmail.com>
CC: Sami Liedes <sliedes@cc.hut.fi>
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/ext2/balloc.c | 29 +++++++++++++++++++++++++++++
1 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index 10bb02c..9104712 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -113,6 +113,17 @@ err_out:
return 0;
}

+static int ext2_block_in_group(struct super_block *sb,
+ unsigned int block_group, ext2_fsblk_t block)
+{
+ if (block < ext2_group_first_block_no(sb, block_group))
+ return 0;
+ if (block >= ext2_group_first_block_no(sb, block_group) +
+ EXT2_BLOCKS_PER_GROUP(sb))
+ return 0;
+ return 1;
+}
+
/*
* Read the bitmap for a given block_group,and validate the
* bits for block/inode/inode tables are set in the bitmaps
@@ -129,6 +140,24 @@ read_block_bitmap(struct super_block *sb, unsigned int block_group)
desc = ext2_get_group_desc(sb, block_group, NULL);
if (!desc)
return NULL;
+ if (!ext2_block_in_group(sb, block_group,
+ le32_to_cpu(desc->bg_block_bitmap)) ||
+ !ext2_block_in_group(sb, block_group,
+ le32_to_cpu(desc->bg_inode_bitmap)) ||
+ !ext2_block_in_group(sb, block_group,
+ le32_to_cpu(desc->bg_inode_table)) ||
+ !ext2_block_in_group(sb, block_group,
+ le32_to_cpu(desc->bg_inode_table) +
+ EXT2_SB(sb)->s_itb_per_group - 1)) {
+ ext2_error(sb, __func__, "Corrupted group descriptor - "
+ "block_group = %u, block_bitmap = %u, "
+ "inode_bitmap = %u, inode_table = %u",
+ block_group,
+ le32_to_cpu(desc->bg_block_bitmap),
+ le32_to_cpu(desc->bg_inode_bitmap),
+ le32_to_cpu(desc->bg_inode_table));
+ return NULL;
+ }
bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
bh = sb_getblk(sb, bitmap_blk);
if (unlikely(!bh)) {
--
1.5.2.4