On Thu, 2 Jul 2026, Benjamin Marzinski wrote:
> 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
Hi
This triggers a warning on 64-bit systems, because 1 (32-bit int) will be
shifted left by 61. I fixed it, no need to resend it.
Mikulas
