FKIE_CVE-2026-64119

Vulnerability from fkie_nvd - Published: 2026-07-19 16:17 - Updated: 2026-07-19 16:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: l2tp: use list_del_rcu in l2tp_session_unhash An unprivileged local user can pin a host CPU indefinitely in l2tp_session_get_by_ifname() by issuing L2TP_CMD_SESSION_GET on L2TP_ATTR_IFNAME concurrently with L2TP_CMD_SESSION_CREATE and L2TP_CMD_SESSION_DELETE on the same tunnel. All three commands take GENL_UNS_ADMIN_PERM, so CAP_NET_ADMIN in the netns user namespace suffices; on any host that has l2tp_core loaded the trigger is reachable from a standard `unshare -Urn` sandbox. l2tp_session_unhash() removes a session from tunnel->session_list with list_del_init(), but that list is walked by l2tp_session_get_by_ifname() with list_for_each_entry_rcu() under rcu_read_lock_bh(). list_del_init() leaves the deleted entry's next/prev self-pointing; a reader that has loaded the entry and then advances pos->list.next reads &session->list, container_of()s back to the same session, and list_for_each_entry_rcu() never reaches the list head. The CPU stays in strcmp() inside the walker, with BH and preemption disabled, so RCU grace periods on the host stall behind it and the wedged thread cannot be killed (SIGKILL is delivered on syscall return). Use list_del_rcu() to match the existing list_add_rcu() in l2tp_session_register(); the deleted session remains visible to in-flight walkers with consistent next/prev pointers until kfree_rcu() in l2tp_session_free() releases it. tunnel->session_list has exactly one list_del_init() call site; the list_del_init (&session->clist) at l2tp_core.c:533 operates on the per-collision list, which is not walked under RCU. list_empty(&session->list) is not used anywhere in net/l2tp/ after the unhash point, so dropping the post-delete self-init is safe; the fix has no userspace-visible behavior change.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5e40919a40cb3e590ed45c2a54a4a2518aa88a99
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/979c017803c40829b03acd9e5236e354b7622360
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/acab6314bb75be994f720ed13e9d9139cbf828a8
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e0c3dd7b30cc5ee42ab502da140cda93d794a20b
Impacted products
Vendor Product Version
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{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/l2tp/l2tp_core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "5e40919a40cb3e590ed45c2a54a4a2518aa88a99",
              "status": "affected",
              "version": "89b768ec2dfefaeba5212de14fc71368e12d06ba",
              "versionType": "git"
            },
            {
              "lessThan": "e0c3dd7b30cc5ee42ab502da140cda93d794a20b",
              "status": "affected",
              "version": "89b768ec2dfefaeba5212de14fc71368e12d06ba",
              "versionType": "git"
            },
            {
              "lessThan": "acab6314bb75be994f720ed13e9d9139cbf828a8",
              "status": "affected",
              "version": "89b768ec2dfefaeba5212de14fc71368e12d06ba",
              "versionType": "git"
            },
            {
              "lessThan": "979c017803c40829b03acd9e5236e354b7622360",
              "status": "affected",
              "version": "89b768ec2dfefaeba5212de14fc71368e12d06ba",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "b3dd82a879f25db9d096ae3053f657aa4260ecc6",
              "versionType": "git"
            },
            {
              "lessThan": "6.12",
              "status": "affected",
              "version": "6.11.3",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/l2tp/l2tp_core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.12"
            },
            {
              "lessThan": "6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.92",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.34",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: use list_del_rcu in l2tp_session_unhash\n\nAn unprivileged local user can pin a host CPU indefinitely in\nl2tp_session_get_by_ifname() by issuing L2TP_CMD_SESSION_GET on\nL2TP_ATTR_IFNAME concurrently with L2TP_CMD_SESSION_CREATE and\nL2TP_CMD_SESSION_DELETE on the same tunnel. All three commands take\nGENL_UNS_ADMIN_PERM, so CAP_NET_ADMIN in the netns user namespace\nsuffices; on any host that has l2tp_core loaded the trigger is\nreachable from a standard `unshare -Urn` sandbox.\n\nl2tp_session_unhash() removes a session from tunnel-\u003esession_list\nwith list_del_init(), but that list is walked by\nl2tp_session_get_by_ifname() with list_for_each_entry_rcu() under\nrcu_read_lock_bh(). list_del_init() leaves the deleted entry\u0027s\nnext/prev self-pointing; a reader that has loaded the entry and\nthen advances pos-\u003elist.next reads \u0026session-\u003elist, container_of()s\nback to the same session, and list_for_each_entry_rcu() never\nreaches the list head. The CPU stays in strcmp() inside the\nwalker, with BH and preemption disabled, so RCU grace periods on\nthe host stall behind it and the wedged thread cannot be killed\n(SIGKILL is delivered on syscall return).\n\nUse list_del_rcu() to match the existing list_add_rcu() in\nl2tp_session_register(); the deleted session remains visible to\nin-flight walkers with consistent next/prev pointers until\nkfree_rcu() in l2tp_session_free() releases it. tunnel-\u003esession_list\nhas exactly one list_del_init() call site; the list_del_init\n(\u0026session-\u003eclist) at l2tp_core.c:533 operates on the per-collision\nlist, which is not walked under RCU. list_empty(\u0026session-\u003elist) is\nnot used anywhere in net/l2tp/ after the unhash point, so dropping\nthe post-delete self-init is safe; the fix has no userspace-visible\nbehavior change."
    }
  ],
  "id": "CVE-2026-64119",
  "lastModified": "2026-07-19T16:17:53.450",
  "metrics": {},
  "published": "2026-07-19T16:17:53.450",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5e40919a40cb3e590ed45c2a54a4a2518aa88a99"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/979c017803c40829b03acd9e5236e354b7622360"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/acab6314bb75be994f720ed13e9d9139cbf828a8"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e0c3dd7b30cc5ee42ab502da140cda93d794a20b"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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