From 9743132a41f4d9d0e54c5f2adcb821b04796bab1 Mon Sep 17 00:00:00 2001 From: Benjamin Marzinski Date: Thu, 2 Jul 2026 21:43:39 -0400 Subject: [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. Signed-off-by: Benjamin Marzinski Signed-off-by: Mikulas Patocka Fixes: c20e36b7631d ("dm log: fix out-of-bounds write due to region_count overflow") Cc: stable@vger.kernel.org --- 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..2ddeb4250c59 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 = 1UL << (BITS_PER_LONG - BYTE_SHIFT); lc->bitset_uint32_count = bitset_size / sizeof(*lc->clean_bits);