[patch 31/50] corrupted cramfs filesystems cause kernel oops (CVE-2006-5823)

[Chris Wright]

-stable review patch.  If anyone has any objections, please let us know.
------------------

From: Phillip Lougher <phillip@xxxxxxxxxxxxxx>

Steve Grubb's fzfuzzer tool (http://people.redhat.com/sgrubb/files/
fsfuzzer-0.6.tar.gz) generates corrupt Cramfs filesystems which cause
Cramfs to kernel oops in cramfs_uncompress_block().  The cause of the oops
is an unchecked corrupted block length field read by cramfs_readpage().

This patch adds a sanity check to cramfs_readpage() which checks that the
block length field is sensible.  The (PAGE_CACHE_SIZE << 1) size check is
intentional, even though the uncompressed data is not going to be larger
than PAGE_CACHE_SIZE, gzip sometimes generates compressed data larger than
the original source data.  Mkcramfs checks that the compressed size is
always less than or equal to PAGE_CACHE_SIZE << 1.  Of course Cramfs could
use the original uncompressed data in this case, but it doesn't.

Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
Date: Thu, 7 Dec 2006 04:37:20 +0000 (-0800)
Subject: [patch 31/50] [PATCH] corrupted cramfs filesystems cause kernel oops
X-Git-Tag: v2.6.20-rc1
X-Git-Url: http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=8bb0269160df2a60764013994d0bc5165406cf4a

 fs/cramfs/inode.c |    2 ++
 1 file changed, 2 insertions(+)

--- linux-2.6.19.1.orig/fs/cramfs/inode.c
+++ linux-2.6.19.1/fs/cramfs/inode.c
@@ -481,6 +481,8 @@ static int cramfs_readpage(struct file *
 		pgdata = kmap(page);
 		if (compr_len == 0)
 			; /* hole */
+		else if (compr_len > (PAGE_CACHE_SIZE << 1))
+			printk(KERN_ERR "cramfs: bad compressed blocksize %u\n", compr_len);
 		else {
 			mutex_lock(&read_mutex);
 			bytes_filled = cramfs_uncompress_block(pgdata,

--
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