linux-kernel - [PATCH 3.16 128/305] Cramfs: fix abad comparison when wrap-arounds occur

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Message-ID: <lsq.1549201508.522109674@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Nicolas Pitre" <nico@...aro.org>,
        "Nicolas Pitre" <nicolas.pitre@...aro.org>,
        "Anatoly Trosinenko" <anatoly.trosinenko@...il.com>
Subject: [PATCH 3.16 128/305] Cramfs: fix abad comparison when
 wrap-arounds occur

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Nicolas Pitre <nicolas.pitre@...aro.org>

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@...il.com>
Signed-off-by: Nicolas Pitre <nico@...aro.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/cramfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -183,7 +183,8 @@ static void *cramfs_read(struct super_bl
 			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;
 	}