Out-of-bounds access occurs if the fast device is expanded unexpectedly
before the first-time resume of the cache table. This happens because
expanding the fast device requires reloading the cache table for
cache_create to allocate new in-core data structures that fit the new
size, and the check in cache_preresume is not performed during the
first resume, leading to the issue.
Reproduce steps:
1. prepare component devices:
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 65536 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
2. load a cache table of 512 cache blocks, and deliberately expand the
fast device before resuming the cache, making the in-core data
structures inadequate.
dmsetup create cache --notable
dmsetup reload cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
dmsetup reload cdata --table "0 131072 linear /dev/sdc 8192"
dmsetup resume cdata
dmsetup resume cache
3. suspend the cache to write out the in-core dirty bitset and hint
array, leading to out-of-bounds access to the dirty bitset at offset
0x40:
dmsetup suspend cache
KASAN reports:
BUG: KASAN: vmalloc-out-of-bounds in is_dirty_callback+0x2b/0x80
Read of size 8 at addr ffffc90000085040 by task dmsetup/90
(...snip...)
The buggy address belongs to the virtual mapping at
[ffffc90000085000, ffffc90000087000) created by:
cache_ctr+0x176a/0x35f0
(...snip...)
Memory state around the buggy address:
ffffc90000084f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90000084f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90000085000: 00 00 00 00 00 00 00 00 f8 f8 f8 f8 f8 f8 f8 f8
^
ffffc90000085080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90000085100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Fix by checking the size change on the first resume.
Signed-off-by: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
Fixes: f494a9c6b1b6 ("dm cache: cache shrinking support")
---
drivers/md/dm-cache-target.c | 37 ++++++++++++++++--------------------
1 file changed, 16 insertions(+), 21 deletions(-)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index fa8ef2c32af8..40709310e327 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2901,24 +2901,24 @@ static dm_cblock_t get_cache_dev_size(struct cache *cache)
static bool can_resize(struct cache *cache, dm_cblock_t new_size)
{
if (from_cblock(new_size) > from_cblock(cache->cache_size)) {
- if (cache->sized) {
- DMERR("%s: unable to extend cache due to missing cache table reload",
- cache_device_name(cache));
- return false;
- }
+ DMERR("%s: unable to extend cache due to missing cache table reload",
+ cache_device_name(cache));
+ return false;
}
/*
* We can't drop a dirty block when shrinking the cache.
*/
- new_size = to_cblock(find_next_bit(cache->dirty_bitset,
- from_cblock(cache->cache_size),
- from_cblock(new_size)));
- if (new_size != cache->cache_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;
+ if (cache->loaded_mappings) {
+ new_size = to_cblock(find_next_bit(cache->dirty_bitset,
+ from_cblock(cache->cache_size),
+ from_cblock(new_size)));
+ if (new_size != cache->cache_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;
+ }
}
return true;
@@ -2949,20 +2949,15 @@ static int cache_preresume(struct dm_target *ti)
/*
* Check to see if the cache has resized.
*/
- if (!cache->sized) {
- r = resize_cache_dev(cache, csize);
- if (r)
- return r;
-
- cache->sized = true;
-
- } else if (csize != cache->cache_size) {
+ if (!cache->sized || csize != cache->cache_size) {
if (!can_resize(cache, csize))
return -EINVAL;
r = resize_cache_dev(cache, csize);
if (r)
return r;
+
+ cache->sized = true;
}
if (!cache->loaded_mappings) {
--
2.47.0
