exit: hold a reference to thread_pid across proc_flush_pid

{
  "id": "839c124f9a761bf83ecd68ed8dbbc3ac4157f69f6b0f376337e55a099edbc840",
  "url": "https://osv.dev/vulnerability/CVE-2026-97903",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "exit: hold a reference to thread_pid across proc_flush_pid",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: exit: hold a reference to thread_pid across proc_flush_pid Commit 0a36bad01731 (\"release_task: kill the no longer needed get/put_pid(thread_pid)\") removed the reference around proc_flush_pid(). It assumed that free_pids(post.pids) at the end of release_task() would keep thread_pid alive until then. That assumption is wrong. __change_pid() only records a detached PID in post.pids when pid_has_task() is false for every PIDTYPE. If another task still uses the exiting task's PID as its process group or session ID, __unhash_process() removes the exiting task's PIDTYPE_PID link but leaves the PID out of post.pids. release_task() therefore holds no reference to it after dropping tasklist_lock. The other task can then remove the remaining PIDTYPE links. Its free_pids() call schedules delayed_put_pid(), and the RCU callback can free the PID before the first release_task() reaches proc_flush_pid(). An unprivileged reproducer races wait4(-1) against setsid() to trigger this ordering. Three of three fresh v7.2 KASAN boots reported: BUG: KASAN: slab-use-after-free in proc_invalidate_siblings_dcache+0x3e2/0x3f0 Read of size 8 by task h7_pid_reaper/1921 Call Trace: proc_invalidate_siblings_dcache release_task wait_consider_task __do_wait do_wait kernel_wait4 Freed by task 0: kmem_cache_free put_pid delayed_put_pid rcu_core Last potentially related work creation: __call_rcu_common free_pids ksys_setsid KASAN identified a 144",
    "evidence": "osv:CVE-2026-97903",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.53",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-97903",
      "aliases": [
        "CVE-2026-97903"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0a36bad01731e71568bdd365764d38b6bd576ab0"
                },
                {
                  "fixed": "bcb0936862f2b653114d9bd582ca26990ef54a64"
                },
                {
                  "fixed": "96803a12e8ac15f0a1b4b151db59038f12304e58"
                },
                {
                  "fixed": "cdd812d0683dee14ead02c9eded568685e61b23f"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97903.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.16.0"
                },
                {
                  "fixed": "6.18.53"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97903.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.571839779Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/96803a12e8ac15f0a1b4b151db59038f12304e58",
        "https://git.kernel.org/stable/c/bcb0936862f2b653114d9bd582ca26990ef54a64",
        "https://git.kernel.org/stable/c/cdd812d0683dee14ead02c9eded568685e61b23f",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97903.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-97903",
        "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/2026/97xxx/CVE-2026-97903.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-97903",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 495423,
  "published_at": "2026-09-25T10:22:29.852+00:00"
}