tracing: Fix NULL pointer dereference in module event cache removal

{
  "id": "94f9d8c76aec2eaa1cebc2acd627725a1571b34bd1a0d743eb43330383171135",
  "url": "https://osv.dev/vulnerability/CVE-2026-74633",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "tracing: Fix NULL pointer dereference in module event cache removal",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: tracing: Fix NULL pointer dereference in module event cache removal A module-only event filter such as \":mod:foo\" is cached with a NULL event_mod->match when foo has not been loaded. If a later write tries to remove a specific match from the same module, remove_cache_mod() passes the NULL cached match to strcmp(), causing a NULL pointer dereference. The issue can be reproduced from userspace: echo ':mod:trace_events_kunit_missing' > /sys/kernel/tracing/set_event echo '!foo_bar:mod:trace_events_kunit_missing' >> /sys/kernel/tracing/set_event The second write must be a concatenation (\">>\") to not include O_TRUNC as that would cause ftrace_clear_events() to clear the cached modules lines. The crash was reproduced on x86_64 QEMU while KUnit workers contended on the event tracing path: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode RIP: 0010:strcmp+0x10/0x30 Call Trace: __ftrace_set_clr_event_nolock+0x373/0x4a0 ftrace_set_clr_event+0xf0/0x180 ftrace_event_write+0xdf/0x110 vfs_write+0xf6/0x440 ksys_write+0x68/0xe0 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f Check event_mod->match before comparing it, consistent with the existing NULL checks for the cached system and event fields. The mismatched removal continues to return -EINVAL; a broad cached module filter is removed with \"!:mod:\".",
    "evidence": "osv:CVE-2026-74633",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.45",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-74633",
      "aliases": [
        "CVE-2026-74633"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "b355247df104ef6644288884afd2c08b7bf49897"
                },
                {
                  "fixed": "152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9"
                },
                {
                  "fixed": "ad4e9dd5fec7a322a471ff36fb9c76214e3c6992"
                },
                {
                  "fixed": "b69859204d4db3acd86c1c2dadcef0d77b451933"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74633.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.14.0"
                },
                {
                  "fixed": "6.18.45"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.1.9"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74633.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:32.152415182Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9",
        "https://git.kernel.org/stable/c/ad4e9dd5fec7a322a471ff36fb9c76214e3c6992",
        "https://git.kernel.org/stable/c/b69859204d4db3acd86c1c2dadcef0d77b451933",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74633.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-74633",
        "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/2026/74xxx/CVE-2026-74633.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-74633",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 498816,
  "published_at": "2026-08-22T15:32:13.808+00:00"
}