dm cache: fix potential out-of-bounds access on the first resume

In the Linux kernel, the following vulnerability has been resolved:

dm cache: fix potential out-of-bounds access on the first resume

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.