[PATCH] 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.

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

Signed-off-by: Roman Smirnov <r.smirnov@omp.ru>
---
 fs/udf/balloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index ab3ffc355949..cd83bbc7d890 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -151,6 +151,13 @@ static void udf_bitmap_free_blocks(struct super_block *sb,
 	block = bloc->logicalBlockNum + offset +
 		(sizeof(struct spaceBitmapDesc) << 3);
 
+	if (block < offset + (sizeof(struct spaceBitmapDesc) << 3)) {
+		udf_debug("integer overflow: %u + %u + %zu",
+			  bloc->logicalBlockNum, offset,
+			  sizeof(struct spaceBitmapDesc) << 3);
+		goto error_return;
+	}
+
 	do {
 		overflow = 0;
 		block_group = block >> (sb->s_blocksize_bits + 3);
-- 
2.34.1