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

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index f408994..6e00039 100644 (file)
--- 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;
        }