drm/amd/display: guard dc_sink dereferences in MST mode validation

{
  "id": "8e578fd8e91900893633e8d74916ade393d0fbf92ba648715f75881563049261",
  "url": "https://osv.dev/vulnerability/CVE-2026-98786",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "drm/amd/display: guard dc_sink dereferences in MST mode validation",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: guard dc_sink dereferences in MST mode validation dm_dp_mst_is_port_support_mode() reads aconnector->dc_sink->dsc_caps... for the DSC branch-throughput check, and get_conv_frl_bw()'s HDMI-PCON FRL-bandwidth path reads aconnector->dc_sink->edid_caps.max_frl_rate, both without a NULL check. dc_sink is cleared asynchronously on MST unplug, and both functions run from paths that the driver's own comments document as racing that teardown: the connector probe worker's ->mode_valid callback and a compositor's atomic check, neither of which holds the MST manager lock that the teardown path uses. The former does have an existing dsc_aux NULL check, but dsc_aux isn't reliably cleared in every path that clears dc_sink, so it doesn't cover this. Fail the port-support check and skip the FRL conversion path when the sink is already gone. (cherry picked from commit 7c3db8da4e039698ae198c870712428644e965c7)",
    "evidence": "osv:CVE-2026-98786",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98786",
      "aliases": [
        "CVE-2026-98786"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "f04d275d94e164d24516c32437c988a323018f63"
                },
                {
                  "fixed": "daa0437fe5e451856aaf8fda602a9fc2105bbd54"
                },
                {
                  "fixed": "217f64f348c90cba62164e7ff38e0ccf78a5ca09"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98786.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.0.0"
                },
                {
                  "fixed": "7.2.10"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98786.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.109889227Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/217f64f348c90cba62164e7ff38e0ccf78a5ca09",
        "https://git.kernel.org/stable/c/daa0437fe5e451856aaf8fda602a9fc2105bbd54",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98786.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98786",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98786.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98786",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 518602,
  "published_at": "2026-10-18T15:48:22.989+00:00"
}