FKIE_CVE-2026-31669

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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": "CVE-2026-31669",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:46.663",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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