bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim

{
  "id": "d86ca12400f2477070cf8b017006dcd4d454fcdb723c4746b1d55a4d495314ab",
  "url": "https://osv.dev/vulnerability/CVE-2026-23319",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim The root cause of this bug is that when 'bpf_link_put' reduces the refcount of 'shim_link->link.link' to zero, the resource is considered released but may still be referenced via 'tr->progs_hlist' in 'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in 'bpf_shim_tramp_link_release' is deferred. During this window, another process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'. Based on Martin KaFai Lau's suggestions, I have created a simple patch. To fix this: Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'. Only increment the refcount if it is not already zero. Testing: I verified the fix by adding a delay in 'bpf_shim_tramp_link_release' to make the bug easier to trigger: static void bpf_shim_tramp_link_release(struct bpf_link *link) { /* ... */ if (!shim_link->trampoline) return; + msleep(100); WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline, NULL)); bpf_trampoline_put(shim_link->trampoline); } Before the patch, running a PoC easily reproduced the crash(almost 100%) with a call trace similar to KaiyanM's report. After the patch, the bug no longer occurs even after millions of iterations.",
    "evidence": "osv:CVE-2026-23319",
    "products": [
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            "evidence": "/affected/1/ranges"
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          {
            "value": "6.18.17",
            "evidence": "/affected/1/ranges"
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            "value": "6.19.7",
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    "severity": "unknown",
    "structured": {
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      "aliases": [
        "CVE-2026-23319"
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      "modified": "2026-10-28T02:30:25.278891353Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2",
        "https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b",
        "https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c",
        "https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b",
        "https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951",
        "https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23319.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23319",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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    "security_relevant": true,
    "severity_evidence": null
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  "source_id": "core-osv",
  "document_id": 491775,
  "published_at": "2026-03-25T10:27:13.678+00:00"
}