kcm: Serialise kcm_sendmsg() for the same socket.

{
  "id": "6a57a0d9fcd63a576e153b6477d2b041aaa9cf3e2f2033ae7441bce7423a93b7",
  "url": "https://osv.dev/vulnerability/CVE-2024-44946",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "kcm: Serialise kcm_sendmsg() for the same socket.",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: kcm: Serialise kcm_sendmsg() for the same socket. syzkaller reported UAF in kcm_release(). [0] The scenario is 1. Thread A builds a skb with MSG_MORE and sets kcm->seq_skb. 2. Thread A resumes building skb from kcm->seq_skb but is blocked by sk_stream_wait_memory() 3. Thread B calls sendmsg() concurrently, finishes building kcm->seq_skb and puts the skb to the write queue 4. Thread A faces an error and finally frees skb that is already in the write queue 5. kcm_release() does double-free the skb in the write queue When a thread is building a MSG_MORE skb, another thread must not touch it. Let's add a per-sk mutex and serialise kcm_sendmsg(). [0]: BUG: KASAN: slab-use-after-free in __skb_unlink include/linux/skbuff.h:2366 [inline] BUG: KASAN: slab-use-after-free in __skb_dequeue include/linux/skbuff.h:2385 [inline] BUG: KASAN: slab-use-after-free in __skb_queue_purge_reason include/linux/skbuff.h:3175 [inline] BUG: KASAN: slab-use-after-free in __skb_queue_purge include/linux/skbuff.h:3181 [inline] BUG: KASAN: slab-use-after-free in kcm_release+0x170/0x4c8 net/kcm/kcmsock.c:1691 Read of size 8 at addr ffff0000ced0fc80 by task syz-executor329/6167 CPU: 1 PID: 6167 Comm: syz-executor329 Tainted: G B 6.8.0-rc5-syzkaller-g9abbc24128bc #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024 Call trace: dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:291 show_stack+0x2c",
    "evidence": "osv:CVE-2024-44946",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "4.19.321",
            "evidence": "/affected/1/ranges"
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      }
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    "severity": "high",
    "structured": {
      "id": "CVE-2024-44946",
      "aliases": [
        "CVE-2024-44946"
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
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      "modified": "2026-10-28T02:30:28.228734848Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/00425508f30baa5ab6449a1f478480ca7cffa6da",
        "https://git.kernel.org/stable/c/6633b17840bf828921254d788ccd15602843fe9b",
        "https://git.kernel.org/stable/c/72da240aafb142630cf16adc803ccdacb3780849",
        "https://git.kernel.org/stable/c/807067bf014d4a3ae2cc55bd3de16f22a01eb580",
        "https://git.kernel.org/stable/c/8c9cdbf600143bd6835c8b8351e5ac956da79aec",
        "https://git.kernel.org/stable/c/9c8d544ed619f704e2b70e63e08ab75630c2ea23",
        "https://git.kernel.org/stable/c/eb06c8d3022ce6738711191c89f9b3e9cfb91914",
        "https://git.kernel.org/stable/c/fa6c23fe6dcac8c8bd63920ee8681292a2bd544e",
        "https://lists.debian.org/debian-lts-announce/2024/10/msg00003.html",
        "https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/44xxx/CVE-2024-44946.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2024-44946",
        "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/2024/44xxx/CVE-2024-44946.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2024-44946",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494560,
  "published_at": "2024-08-31T13:22:47.25+00:00"
}