[PATCH] Check input buffer size in zisofs

Add fakey 'deflateBound()' function to the in-kernel zlib routines

It's not the real deflateBound() in newer zlib libraries, partly because
the upcoming usage of it won't have the "stream" available, so we can't
have the same interfaces anyway.

This uses the new deflateBound() thing to sanity-check the input to the
zlib decompressor before we even bother to start reading in the blocks.

Problem noted by Tim Yamin <plasmaroo@gentoo.org>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

fs/isofs/compress.c

@@ -129,8 +129,14 @@ static int zisofs_readpage(struct file *file, struct page *page)
 	cend = le32_to_cpu(*(__le32 *)(bh->b_data + (blockendptr & bufmask)));
 	brelse(bh);
 
+	if (cstart > cend)
+		goto eio;
+		
 	csize = cend-cstart;
 
+	if (csize > deflateBound(1UL << zisofs_block_shift))
+		goto eio;
+
 	/* Now page[] contains an array of pages, any of which can be NULL,
 	   and the locks on which we hold.  We should now read the data and
 	   release the pages.  If the pages are NULL the decompressed data

include/linux/zlib.h

@@ -506,6 +506,11 @@ extern int zlib_deflateReset (z_streamp strm);
    stream state was inconsistent (such as zalloc or state being NULL).
 */
 
+static inline unsigned long deflateBound(unsigned long s)
+{
+	return s + ((s + 7) >> 3) + ((s + 63) >> 6) + 11;
+}
+
 extern int zlib_deflateParams (z_streamp strm, int level, int strategy);
 /*
      Dynamically update the compression level and compression strategy.  The