# CVE-2026-31458: mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

Status: published. Published: 2026-04-22. Updated: 2026-11-05.

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

mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

Multiple sysfs command paths dereference contexts_arr[0] without first
verifying that kdamond->contexts->nr == 1.  A user can set nr_contexts to
0 via sysfs while DAMON is running, causing NULL pointer dereferences.

In more detail, the issue can be triggered by privileged users like
below.

First, start DAMON and make contexts directory empty
(kdamond->contexts->nr == 0).

    # damo start
    # cd /sys/kernel/mm/damon/admin/kdamonds/0
    # echo 0 > contexts/nr_contexts

Then, each of below commands will cause the NULL pointer dereference.

    # echo update_schemes_stats > state
    # echo update_schemes_tried_regions > state
    # echo update_schemes_tried_bytes > state
    # echo update_schemes_effective_quotas > state
    # echo update_tuned_intervals > state

Guard all commands (except OFF) at the entry point of
damon_sysfs_handle_cmd().

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 0ac32b8affb5a384253dbb8339bd2d0e91add0b7; < aba546061341b56e9ffb37e1eb661a3628b6ec12 (affected, git); ≥ 0ac32b8affb5a384253dbb8339bd2d0e91add0b7; < 1e8da792672481d603fa7cd0d815577220a3ee27 (affected, git); ≥ 0ac32b8affb5a384253dbb8339bd2d0e91add0b7; < 708033c231bd782858f4ddbb46ee874a5a5fbdab (affected, git); ≥ 0ac32b8affb5a384253dbb8339bd2d0e91add0b7; < bbe03ad3fb9e714191757ca7b41582f930be7be2 (affected, git); ≥ 0ac32b8affb5a384253dbb8339bd2d0e91add0b7; < 1bfe9fb5ed2667fb075682408b776b5273162615 (affected, git). Source: CNA: Linux
- Linux / Linux: 5.18 (affected); ≥ 0; < 5.18 (unaffected, semver); ≥ 6.6.131; ≤ 6.6.* (unaffected, semver); ≥ 6.12.80; ≤ 6.12.* (unaffected, semver); ≥ 6.18.21; ≤ 6.18.* (unaffected, semver); ≥ 6.19.11; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-05; percentile 1.99%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/aba546061341b56e9ffb37e1eb661a3628b6ec12 (CNA: Linux)

- https://git.kernel.org/stable/c/1e8da792672481d603fa7cd0d815577220a3ee27 (CNA: Linux)

- https://git.kernel.org/stable/c/708033c231bd782858f4ddbb46ee874a5a5fbdab (CNA: Linux)

- https://git.kernel.org/stable/c/bbe03ad3fb9e714191757ca7b41582f930be7be2 (CNA: Linux)

- https://git.kernel.org/stable/c/1bfe9fb5ed2667fb075682408b776b5273162615 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-31458; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-31458; retrieved 2026-11-05; source updated Not reported

Revision: 62cf719072b35c874003003b8ae2acef294f52a0129d39483128c932a4e3198f

Canonical: https://y2.dev/cve/CVE-2026-31458

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