[PATCH] dm-log: fix a bitset_size overflow on 32bit machines

Commit c20e36b7631d ("dm log: fix out-of-bounds write due to
region_count overflow") made sure that region_count could fit in an
unsigned int. But the bitmap memory isn't allocated based on
region_count. It uses bitset_size (a size_t variable). The first step of
calculating bitset_size is to set it to region_count, rounded up to a
multiple of BITS_PER_LONG. If region_size is less than BITS_PER_LONG
smaller than UINT_MAX, it will get rounded up to 2^32. On a 32bit
architecture, this will make bitset_size wrap around to 0 and fail,
despite region_count being valid.

Since bitset_size gets divided by 8, it can hold any valid region_count.
It just needs a special case to handle the rollover. If it is 0, the
value rolled over, and bitset size should be set to the number of bytes
needed to hold 2^32 bits.

Fixes: c20e36b7631d ("dm log: fix out-of-bounds write due to region_count overflow")
Signed-off-by: Benjamin Marzinski <[email protected]>
---
 drivers/md/dm-log.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index d316757a328b..77a0ee186aab 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -425,6 +425,9 @@ static int create_log_context(struct dm_dirty_log *log, struct dm_target *ti,
 	 */
 	bitset_size = dm_round_up(region_count, BITS_PER_LONG);
 	bitset_size >>= BYTE_SHIFT;
+	/* Handle dm_round_up rollover on 32-bit systems */
+	if (!bitset_size)
+		bitset_size = 1 << (BITS_PER_LONG - BYTE_SHIFT);
 
 	lc->bitset_uint32_count = bitset_size / sizeof(*lc->clean_bits);
 
-- 
2.53.0