[PATCH v2] udf: balloc: prevent integer overflow in udf_bitmap_free_blocks()

[Roman Smirnov <r.smirnov@omp.ru>]

An overflow may occur if the function is called with the last
block and an offset greater than zero. It is necessary to add
a check to avoid this.

Overflow is also possible when we sum offset and
sizeof(struct spaceBitmapDesc) << 3. For this reason it
is necessary to check overflow of this too. The result is
stored in total_offset.

Found by Linux Verification Center (linuxtesting.org) with Svace.

Suggested-by: Jan Kara <jack@suse.com>
Signed-off-by: Roman Smirnov <r.smirnov@omp.ru>
---
 V1 -> V2: Overflow checks have been replaced by functions

 fs/udf/balloc.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index ab3ffc355949..4bf2720111f1 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -18,6 +18,7 @@
 #include "udfdecl.h"
 
 #include <linux/bitops.h>
+#include <linux/overflow.h>
 
 #include "udf_i.h"
 #include "udf_sb.h"
@@ -133,6 +134,7 @@ static void udf_bitmap_free_blocks(struct super_block *sb,
 	unsigned long block;
 	unsigned long block_group;
 	unsigned long bit;
+	unsigned int total_offset;
 	unsigned long i;
 	int bitmap_nr;
 	unsigned long overflow;
@@ -140,17 +142,20 @@ 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 + count < count ||
-	    (bloc->logicalBlockNum + count) > partmap->s_partition_len) {
-		udf_debug("%u < %d || %u + %u > %u\n",
+	    (bloc->logicalBlockNum + count) > partmap->s_partition_len ||
+	    check_add_overflow(offset,
+			       sizeof(struct spaceBitmapDesc) << 3, &total_offset) ||
+	    check_add_overflow(bloc->logicalBlockNum, total_offset, &block)) {
+		udf_debug("%u < %d || %u + %u > %u || %u + %zu > %u || %u + %u + %zu > %u\n",
 			  bloc->logicalBlockNum, 0,
 			  bloc->logicalBlockNum, count,
-			  partmap->s_partition_len);
+			  partmap->s_partition_len,
+			  offset, sizeof(struct spaceBitmapDesc) << 3, UINT_MAX,
+			  bloc->logicalBlockNum, offset,
+			  sizeof(struct spaceBitmapDesc) << 3, UINT_MAX);
 		goto error_return;
 	}
 
-	block = bloc->logicalBlockNum + offset +
-		(sizeof(struct spaceBitmapDesc) << 3);
-
 	do {
 		overflow = 0;
 		block_group = block >> (sb->s_blocksize_bits + 3);
-- 
2.34.1