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>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 355c522..a6c9c2d 100644 (file)
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -185,7 +185,8 @@ 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;
        }