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CVE-2026-80961
dm-pcache: validate kset key_num and intra-segment bounds
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/md. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-80961 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Two more fields decoded from the cache device go unbounded. The kset key_num drives cache_kset_crc() and the replay loop in cache_replay(), the writeback worker and the GC worker, but only the magic and a fixed-seed CRC are checked first, so a non-last kset whose key_num exceeds the PCACHE_KSET_KEYS_MAX buffer reads past its end before the CRC compare. A key's intra-segment offset and length in cache_key_decode() are taken verbatim, so a key running past its segment is replayed into the cache tree and the data CRC check and every later read hit then copy adjacent persistent memory into the caller's bio -- an out-of-bounds read that leaks to user space. Both fields are controlled by whoever supplies the cache device (CAP_SYS_ADMIN); the CRC seed is public. Add kset_onmedia_valid() to bound key_num before any kset read, and reject a key whose offset plus length, computed in 64 bits, exceeds the segment data_size. Valid metadata is unaffected.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/md/dm-pcache/cache.h
drivers/md/dm-pcache/cache_gc.c
drivers/md/dm-pcache/cache_key.c
drivers/md/dm-pcache/cache_writeback.c
- What this is
- DEVICE-MAPPER PCACHE TARGETMAINTAINERS section matched on drivers/md/dm-pcache/ · dm-devel@lists.linux.dev · Maintained
Check it on the machine
grep -wE 'CONFIG_DM_PCACHE|CONFIG_MD' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code in 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_DM_PCACHE, CONFIG_MD
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/md
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.18 | 6.18.50 | d8caf96040a0 |
| 6.18 | 7.2.4 | 5ac38f4b4862 |
| 6.18 | 7.3 | f11deb032fd8 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bugs are reached only via local device-mapper ioctls on /dev/mapper/control (ctl_ioctl → table_load → dm_pcache_ctr → pcache_cache_start → cache_replay) and the subsequent local GC/writeback workers and bio map path; no network protocol or physical-bus input feeds kset/key decode.
- AC:LAttack complexity, low
- The attacker fully controls the DAX cache image; kset CRC uses public PCACHE_CRC_SEED 0x3B15A, so a non-last kset with key_num > 128 and keys whose cache_seg_off+len exceed the segment are encoded and replayed deterministically on table load with no race or victim-side state.
- PR:LPrivileges required, low
- ctl_ioctl gates DM_TABLE_LOAD with capable(CAP_SYS_ADMIN), which per kernel CNA guidance is obtainable inside an unprivileged user namespace and in storage containers with delegated mapper/DAX nodes, so this is Low rather than init-namespace root only.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own dmsetup/DM_TABLE_LOAD of a pcache target whose cache device holds crafted INIT_DONE ksets, then optional reads of the mapped device; no separate victim must mount media or open files.
- S:UScope, unchanged
- The out-of-bounds kset/key access corrupts and discloses memory inside the host kernel that loaded the pcache table; it does not cross a VM, hypervisor, IOMMU, or other separate security-authority boundary.
- C:HConfidentiality impact, high
- cache_kset_crc() reads struct_size(..., key_num) bytes from a buffer sized for 128 keys, an unbounded kernel-heap OOB read; keys with unchecked cache_seg_off+len are then copied by segment_copy_to_bio() from adjacent pmem/kernel memory into the caller's bio, leaking to userspace.
- I:HIntegrity impact, high
- Replay inserts those OOB keys into the cache tree; writeback then copies from the attacker-chosen cache addresses onto the backing device, and later cut/advance of those keys operates on corrupted cache_pos. This OOB memory-corruption class is Integrity High under kernel CNA guidance.
- A:HAvailability impact, high
- An oversized key_num makes crc32c walk off the kset buffer into unmapped heap, writeback BUG_ON(seg_remain < key->len), and cache_pos_advance() BUG_ON or a copy past the DAX mapping can oops or panic the kernel, causing system-wide denial of service.