[PATCH 4.9 127/141] Cramfs: fix abad comparison when wrap-arounds occur

From: Greg Kroah-Hartman
Date: Sun Nov 11 2018 - 17:37:50 EST


4.9-stable review patch. If anyone has any objections, please let me know.

------------------

From: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/cramfs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -186,7 +186,8 @@ static void *cramfs_read(struct super_bl
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;
}