From 21e6710a43292bce88cb533db1cdc08008d166a0 Mon Sep 17 00:00:00 2001
From: Nicolas Pitre <nicolas.pitre@linaro.org>
Date: Tue, 30 Oct 2018 13:26:15 -0400
Subject: [PATCH] Cramfs: fix abad comparison when wrap-arounds occur

commit 672ca9dd13f1aca0c17516f76fc5b0e8344b3e46 upstream.

It is possible for corrupted filesystem images to produce very large
block offsets that may wrap when a length is added, and wrongly pass
the buffer size test.

Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/cramfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index ddcfe590b8a8..dd12099e3d5e 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -183,7 +183,8 @@ static void *cramfs_read(struct super_block *sb, unsigned int offset, unsigned i
 			continue;
 		blk_offset = (blocknr - buffer_blocknr[i]) << PAGE_CACHE_SHIFT;
 		blk_offset += offset;
-		if (blk_offset + len > BUFFER_SIZE)
+		if (blk_offset > BUFFER_SIZE ||
+		    blk_offset + len > BUFFER_SIZE)
 			continue;
 		return read_buffers[i] + blk_offset;
 	}