dm mirror log: round up region bitmap size to BITS_PER_LONG

The code in dm-log rounds up bitset_size to 32 bits. It then uses
find_next_zero_bit_le on the allocated region. find_next_zero_bit_le
accesses the bitmap using unsigned long pointers. So, on 64-bit
architectures, it may access 4 bytes beyond the allocated size.

Fix this bug by rounding up bitset_size to BITS_PER_LONG.

This bug was found by running the lvm2 testsuite with kasan.

Fixes: 29121bd ("[PATCH] dm mirror log: bitset_size fix")
Cc: [email protected]
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>

drivers/md/dm-log.c

@@ -415,8 +415,7 @@ static int create_log_context(struct dm_dirty_log *log, struct dm_target *ti,
 	/*
 	 * Work out how many "unsigned long"s we need to hold the bitset.
 	 */
-	bitset_size = dm_round_up(region_count,
-				  sizeof(*lc->clean_bits) << BYTE_SHIFT);
+	bitset_size = dm_round_up(region_count, BITS_PER_LONG);
 	bitset_size >>= BYTE_SHIFT;
 
 	lc->bitset_uint32_count = bitset_size / sizeof(*lc->clean_bits);