linux-kernel - [patch] udf: potential integer overflow

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Date:	Mon, 15 Mar 2010 11:21:13 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Hannes Eder <hannes@...neseder.net>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch] udf: potential integer overflow

bloc->logicalBlockNum is unsigned so it's never less than zero.

When I saw that, it made me worry that "bloc->logicalBlockNum + count"
could overflow.  That's why I changed the check for less than zero
to an overflow check.  (The test works because "count" is also 
unsigned.)

Signed-off-by: Dan Carpenter <error27@...il.com>
---
GCC 4.1 apparently optimizes overflow checks like this away, but it should
work for other versions of gcc.  I tested with GCC 4.3.
http://www.fefe.de/intof.html

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index 19626e2..9a9378b 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -125,9 +125,8 @@ static void udf_bitmap_free_blocks(struct super_block *sb,
 
 	mutex_lock(&sbi->s_alloc_mutex);
 	partmap = &sbi->s_partmaps[bloc->partitionReferenceNum];
-	if (bloc->logicalBlockNum < 0 ||
-	    (bloc->logicalBlockNum + count) >
-		partmap->s_partition_len) {
+	if (bloc->logicalBlockNum + count < count ||
+	    (bloc->logicalBlockNum + count) > partmap->s_partition_len) {
 		udf_debug("%d < %d || %d + %d > %d\n",
 			  bloc->logicalBlockNum, 0, bloc->logicalBlockNum,
 			  count, partmap->s_partition_len);
@@ -393,9 +392,8 @@ static void udf_table_free_blocks(struct super_block *sb,
 
 	mutex_lock(&sbi->s_alloc_mutex);
 	partmap = &sbi->s_partmaps[bloc->partitionReferenceNum];
-	if (bloc->logicalBlockNum < 0 ||
-	    (bloc->logicalBlockNum + count) >
-		partmap->s_partition_len) {
+	if (bloc->logicalBlockNum + count < count ||
+	    (bloc->logicalBlockNum + count) > partmap->s_partition_len) {
 		udf_debug("%d < %d || %d + %d > %d\n",
 			  bloc->logicalBlockNum, 0, bloc->logicalBlockNum, count,
 			  partmap->s_partition_len);
--
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