ack
On Tue, Oct 22, 2024 at 8:13 AM Ming-Hung Tsai <mtsai@xxxxxxxxxx> wrote:
>
> dm-cache checks the dirty bits of the cache blocks to be dropped when
> shrinking the fast device, but an index bug in bitset iteration causes
> out-of-bounds access.
>
> Reproduce steps:
>
> 1. create a cache device of 1024 cache blocks (128 bytes dirty bitset)
>
> dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
> dmsetup create cdata --table "0 131072 linear /dev/sdc 8192"
> dmsetup create corig --table "0 524288 linear /dev/sdc 262144"
> dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
> dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \
> /dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
>
> 2. shrink the fast device to 512 cache blocks, triggering out-of-bounds
> access to the dirty bitset (offset 0x80)
>
> dmsetup suspend cache
> dmsetup reload cdata --table "0 65536 linear /dev/sdc 8192"
> dmsetup resume cdata
> dmsetup resume cache
>
> KASAN reports:
>
> BUG: KASAN: vmalloc-out-of-bounds in cache_preresume+0x269/0x7b0
> Read of size 8 at addr ffffc900000f3080 by task dmsetup/131
>
> (...snip...)
> The buggy address belongs to the virtual mapping at
> [ffffc900000f3000, ffffc900000f5000) created by:
> cache_ctr+0x176a/0x35f0
>
> (...snip...)
> Memory state around the buggy address:
> ffffc900000f2f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> ffffc900000f3000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffffc900000f3080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> ^
> ffffc900000f3100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> ffffc900000f3180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>
> Fix by making the index post-incremented.
>
> Signed-off-by: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
> Fixes: f494a9c6b1b6 ("dm cache: cache shrinking support")
> ---
> drivers/md/dm-cache-target.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
> index 68e9a1abd303..1fcd8c5c220e 100644
> --- a/drivers/md/dm-cache-target.c
> +++ b/drivers/md/dm-cache-target.c
> @@ -2912,13 +2912,13 @@ static bool can_resize(struct cache *cache, dm_cblock_t new_size)
> * We can't drop a dirty block when shrinking the cache.
> */
> while (from_cblock(new_size) < from_cblock(cache->cache_size)) {
> - new_size = to_cblock(from_cblock(new_size) + 1);
> if (is_dirty(cache, new_size)) {
> DMERR("%s: unable to shrink cache; cache block %llu is dirty",
> cache_device_name(cache),
> (unsigned long long) from_cblock(new_size));
> return false;
> }
> + new_size = to_cblock(from_cblock(new_size) + 1);
> }
>
> return true;
> --
> 2.47.0
>
