corrupted cramfs filesystems cause kernel oops (CVE-2006-5823)

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@lougher.org.uk>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 8ad52f5bf25551c66ac654ab4f58ffa45fb2860c..30fdd5dc73bd1cd89586f2f99499401ab6fbf292 100644 (file)
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -482,6 +482,8 @@ static int cramfs_readpage(struct file *file, struct page * page)
                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 {
                        down(&read_mutex);
                        bytes_filled = cramfs_uncompress_block(pgdata,