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

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Commit c20e36b763 ("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 <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: c20e36b763 ("dm log: fix out-of-bounds write due to region_count overflow")
Cc: stable@vger.kernel.org
This commit is contained in:
Benjamin Marzinski 2026-07-02 21:43:39 -04:00 committed by Mikulas Patocka
parent 8cdeaa50ea
commit 9743132a41
1 changed files with 3 additions and 0 deletions
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3
drivers/md/dm-log.c
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@ -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);