Cramfs: fix abad comparison when wrap-arounds occur

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>
Cc: stable@vger.kernel.org

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index f408994fc632..6e000392e4a4 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -202,7 +202,8 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
                         continue;
                 blk_offset = (blocknr - buffer_blocknr[i]) << PAGE_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;
         }