CVE-2025-38066

In 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:

1. 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> 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

2. wipe the second array block of the mapping array to simulate data degradations.

mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192 2>/dev/null | hexdump -e 1/8 %un) ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056)) 2>/dev/null | hexdump -e 1/8 %un) dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock

3. 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

4. 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.

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• 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