GHSA-XG7Q-JPQP-FC7G

Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-18 18:31
VLAI
Details

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

bpf: Fix out-of-bounds read of rtt_min in sock_ops

A sockops prog reading skops->rtt_min never checks the sk type: on the tcp_conn_request() path sock_ops->sk is a request_sock (non-full), and the ctx rewrite casts it to a tcp_sock (full) and reads rtt_min past the end of the request_sock, returning dirty adjacent memory.

SEC("sockops")
int prog(struct bpf_sock_ops *skops)
{
    switch (skops->op) {
    case BPF_SOCK_OPS_RWND_INIT:
        leak = skops->rtt_min;   /* reads the request_sock OOB */
    ...
    }
}

For instance one such read returned rtt_min=0xffff8881, the high half of a leaked kernel pointer.

Guarding that cast is exactly what SOCK_OPS_GET_FIELD() does -- it checks is_locked_tcp_sock and returns 0 when sock_ops->sk is not a locked full socket. Every other tcp_sock field in sock_ops goes through it; rtt_min is the only one open-coded, so it skips the check.

Read rtt_min through SOCK_OPS_GET_FIELD() too. rtt_min is a bit special: it is a struct minmax and we only want the current min, so pass rtt_min.s[0].v. That is equivalent to the old hand-computed offset

offsetof(struct tcp_sock, rtt_min) + sizeof_field(struct minmax_sample, t)

(s[0] sits at rtt_min + 0 and .v at + sizeof(.t), i.e. what minmax_get() returns), so the loaded field is unchanged and only the full-sock guard is added. The two BUILD_BUG_ON()s that protected the hand-computed offset are no longer needed.

Before patch:

0: r1 = *(u64 *)(r1 +0)      ; r1 = skops->sk
1: r1 = *(u32 *)(r1 +2324)   ; ((tcp_sock *)sk)->rtt_min.s[0].v

After patch:

0: *(u64 *)(r1 +56) = r9
1: r9 = *(u8 *)(r1 +50)      ; is_locked_tcp_sock
2: if r9 == 0 goto pc+4      ; not a locked full sock -> 0
3: r9 = *(u64 *)(r1 +56)
4: r1 = *(u64 *)(r1 +0)      ; r1 = skops->sk
5: r1 = *(u32 *)(r1 +2324)   ; rtt_min.s[0].v
6: goto pc+2
7: r9 = *(u64 *)(r1 +56)
8: r1 = 0
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{
  "affected": [],
  "aliases": [
    "CVE-2026-98643"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-18T16:17:17Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix out-of-bounds read of rtt_min in sock_ops\n\nA sockops prog reading skops-\u003ertt_min never checks the sk type: on the\ntcp_conn_request() path sock_ops-\u003esk is a request_sock (non-full), and the\nctx rewrite casts it to a tcp_sock (full) and reads rtt_min past the end of\nthe request_sock, returning dirty adjacent memory.\n\n\tSEC(\"sockops\")\n\tint prog(struct bpf_sock_ops *skops)\n\t{\n\t\tswitch (skops-\u003eop) {\n\t\tcase BPF_SOCK_OPS_RWND_INIT:\n\t\t\tleak = skops-\u003ertt_min;   /* reads the request_sock OOB */\n\t\t...\n\t\t}\n\t}\n\nFor instance one such read returned rtt_min=0xffff8881, the high half of a\nleaked kernel pointer.\n\nGuarding that cast is exactly what SOCK_OPS_GET_FIELD() does -- it checks\nis_locked_tcp_sock and returns 0 when sock_ops-\u003esk is not a locked full\nsocket. Every other tcp_sock field in sock_ops goes through it; rtt_min is\nthe only one open-coded, so it skips the check.\n\nRead rtt_min through SOCK_OPS_GET_FIELD() too. rtt_min is a bit special:\nit is a struct minmax and we only want the current min, so pass\nrtt_min.s[0].v. That is equivalent to the old hand-computed offset\n\n\toffsetof(struct tcp_sock, rtt_min) + sizeof_field(struct minmax_sample, t)\n\n(s[0] sits at rtt_min + 0 and .v at + sizeof(.t), i.e. what minmax_get()\nreturns), so the loaded field is unchanged and only the full-sock guard is\nadded. The two BUILD_BUG_ON()s that protected the hand-computed offset\nare no longer needed.\n\nBefore patch:\n\n\t0: r1 = *(u64 *)(r1 +0)      ; r1 = skops-\u003esk\n\t1: r1 = *(u32 *)(r1 +2324)   ; ((tcp_sock *)sk)-\u003ertt_min.s[0].v\n\nAfter patch:\n\n\t0: *(u64 *)(r1 +56) = r9\n\t1: r9 = *(u8 *)(r1 +50)      ; is_locked_tcp_sock\n\t2: if r9 == 0 goto pc+4      ; not a locked full sock -\u003e 0\n\t3: r9 = *(u64 *)(r1 +56)\n\t4: r1 = *(u64 *)(r1 +0)      ; r1 = skops-\u003esk\n\t5: r1 = *(u32 *)(r1 +2324)   ; rtt_min.s[0].v\n\t6: goto pc+2\n\t7: r9 = *(u64 *)(r1 +56)\n\t8: r1 = 0",
  "id": "GHSA-xg7q-jpqp-fc7g",
  "modified": "2026-10-18T18:31:57Z",
  "published": "2026-10-18T18:31:57Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98643"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0c796efa919f52f788c22c79d1f1b70321696b3d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3a46f14e6cf375f3ca38f8f6e6524749e24ea0a8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6785313d4fac96afb21ef193610c1fa88b1a9e64"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/75f8cf22463d82bb1fb0239a3d485fc8f4c8ef03"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a8a9becbac93a9f54f4d565f1f3005eb08a7912f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/cba54d142c43ec96d8c4d566f66439e8c0afded7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fc9d0e6e9d86fbefe7b8fe6ee49f4cf102add79d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fd6bf2721933d8c90bc4ce57f3e204c9295e7e3f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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