GHSA-29W7-PV74-WPQ7

Vulnerability from github – Published: 2026-04-24 15:32 – Updated: 2026-04-24 15:32
VLAI?
Details

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

mptcp: fix slab-use-after-free in __inet_lookup_established

The ehash table lookups are lockless and rely on SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability during RCU read-side critical sections. Both tcp_prot and tcpv6_prot have their slab caches created with this flag via proto_register().

However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into tcpv6_prot_override during inet_init() (fs_initcall, level 5), before inet6_init() (module_init/device_initcall, level 6) has called proto_register(&tcpv6_prot). At that point, tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab remains NULL permanently.

This causes MPTCP v6 subflow child sockets to be allocated via kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so when these sockets are freed without SOCK_RCU_FREE (which is cleared for child sockets by design), the memory can be immediately reused. Concurrent ehash lookups under rcu_read_lock can then access freed memory, triggering a slab-use-after-free in __inet_lookup_established.

Fix this by splitting the IPv6-specific initialization out of mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called from mptcp_proto_v6_init() before protocol registration. This ensures tcpv6_prot_override.slab correctly inherits the SLAB_TYPESAFE_BY_RCU slab cache.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-31669"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-24T15:16:46Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix slab-use-after-free in __inet_lookup_established\n\nThe ehash table lookups are lockless and rely on\nSLAB_TYPESAFE_BY_RCU to guarantee socket memory stability\nduring RCU read-side critical sections. Both tcp_prot and\ntcpv6_prot have their slab caches created with this flag\nvia proto_register().\n\nHowever, MPTCP\u0027s mptcp_subflow_init() copies tcpv6_prot into\ntcpv6_prot_override during inet_init() (fs_initcall, level 5),\nbefore inet6_init() (module_init/device_initcall, level 6) has\ncalled proto_register(\u0026tcpv6_prot). At that point,\ntcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab\nremains NULL permanently.\n\nThis causes MPTCP v6 subflow child sockets to be allocated via\nkmalloc (falling into kmalloc-4k) instead of the TCPv6 slab\ncache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so\nwhen these sockets are freed without SOCK_RCU_FREE (which is\ncleared for child sockets by design), the memory can be\nimmediately reused. Concurrent ehash lookups under\nrcu_read_lock can then access freed memory, triggering a\nslab-use-after-free in __inet_lookup_established.\n\nFix this by splitting the IPv6-specific initialization out of\nmptcp_subflow_init() into a new mptcp_subflow_v6_init(), called\nfrom mptcp_proto_v6_init() before protocol registration. This\nensures tcpv6_prot_override.slab correctly inherits the\nSLAB_TYPESAFE_BY_RCU slab cache.",
  "id": "GHSA-29w7-pv74-wpq7",
  "modified": "2026-04-24T15:32:37Z",
  "published": "2026-04-24T15:32:37Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31669"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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