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Subject[patch 31/50] corrupted cramfs filesystems cause kernel oops (CVE-2006-5823)
-stable review patch.  If anyone has any objections, please let us know.
From: Phillip Lougher <>

Steve Grubb's fzfuzzer tool (
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 <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Chris Wright <>
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
fs/cramfs/inode.c | 2 ++
1 file changed, 2 insertions(+)
--- linux-
+++ linux-
@@ -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 {
bytes_filled = cramfs_uncompress_block(pgdata,
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