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
