NuytsTech Security

CVE-2024-50278

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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.

More information : https://git.kernel.org/stable/c/036dd6e3d2638103e0092864577ea1d091466b86

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