CVE-2025-38066: dm cache: prevent BUG_ON by blocking retries on failed device resumes

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

dm cache: prevent BUGON 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 BUGON 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 cacherestore v1.0 to build the metadata.

cat <<EOF >> cmeta.xml <superblock uuid="" blocksize="128" nrcacheblocks="512" \ policy="smq" hintwidth="4"> <mappings> <mapping cacheblock="0" originblock="0" dirty="false"/> </mappings> </superblock> EOF dmsetup create cmeta --table "0 8192 linear /dev/sdc 0" cacherestore -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.

mappingroot=$(dd if=/dev/sdc bs=1c count=8 skip=192 \ 2>/dev/null | hexdump -e '1/8 "%u\n"') ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096mappingroot+2056)) \ 2>/dev/null | hexdump -e '1/8 "%u\n"') dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$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 BUGON 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:smqloadmapping+0x3e5/0x570

Fix by disallowing resume operations for devices that failed the initial attempt.