CVE-2025-38066 — linux / linux_kernel
Reachable AssertionIn the Linux kernel, the following vulnerability has been resolved:
dm cache: prevent BUG_ON by blocking retries on failed device resumes
A cache device failing to resume due to mapping errors should not be retried, as the failure leaves a partially initialized policy object. Repeating the resume operation risks triggering BUG_ON when reloading cache mappings into the incomplete policy object.
Reproduce steps:
- create a cache metadata consisting of 512 or more cache blocks, with some mappings stored in the first array block of the mapping array. Here we use cache_restore v1.0 to build the metadata.
cat <<EOF >> cmeta.xml
<superblock uuid="" block_size="128" nr_cache_blocks="512"
policy="smq" hint_width="4">
<mappings>
<mapping cache_block="0" origin_block="0" dirty="false"/>
</mappings>
</superblock>
EOF
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
cache_restore -i cmeta.xml -o /dev/mapper/cmeta --metadata-version=2
dmsetup remove cmeta
- wipe the second array block of the mapping array to simulate data degradations.
mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192
2>/dev/null | hexdump -e '1/8 "%u\n"')
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056))
2>/dev/null | hexdump -e '1/8 "%u\n"')
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock
- try bringing up the cache device. The resume is expected to fail due to the broken array block.
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"
dmsetup create cache --notable
dmsetup load cache --table "0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
dmsetup resume cache
- try resuming the cache again. An unexpected BUG_ON is triggered while loading cache mappings.
dmsetup resume cache
Kernel logs:
(snip) ------------[ cut here ]------------ kernel BUG at drivers/md/dm-cache-policy-smq.c:752! Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 0 UID: 0 PID: 332 Comm: dmsetup Not tainted 6.13.4 #3 RIP: 0010:smq_load_mapping+0x3e5/0x570
Fix by disallowing resume operations for devices that failed the initial attempt.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | - | 5.4.294 |
| linux / linux_kernel | 5.5 | 5.10.238 |
| linux / linux_kernel | 5.11 | 5.15.185 |
| linux / linux_kernel | 5.16 | 6.1.141 |
| linux / linux_kernel | 6.2 | 6.6.93 |
| linux / linux_kernel | 6.7 | 6.12.31 |
| linux / linux_kernel | 6.13 | 6.14.9 |
| debian / debian_linux | 11.0 | 11.0.x |
- https://git.kernel.org/stable/c/00586b78eeb7c626a14ca13453a1631f88a7cf36
- https://git.kernel.org/stable/c/025c8f477625eb39006ded650e7d027bcfb20e79
- https://git.kernel.org/stable/c/3986ef4a9b6a0d9c28bc325d8713beba5e67586f
- https://git.kernel.org/stable/c/5da692e2262b8f81993baa9592f57d12c2703dea
- https://git.kernel.org/stable/c/c5356a5e80442131e2714d0d26bb110590e4e568
- https://git.kernel.org/stable/c/c614584c2a66b538f469089ac089457a34590c14
- https://git.kernel.org/stable/c/cc80a5cc520939d0a7d071cc4ae4b3c55ef171d0
- https://git.kernel.org/stable/c/f3128e3074e8af565cc6a66fe3384a56df87f803
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
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