FKIE_CVE-2026-23319

Vulnerability from fkie_nvd - Published: 2026-03-25 11:16 - Updated: 2026-03-25 15:41
Severity ?
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when \u0027bpf_link_put\u0027 reduces the\nrefcount of \u0027shim_link-\u003elink.link\u0027 to zero, the resource is considered\nreleased but may still be referenced via \u0027tr-\u003eprogs_hlist\u0027 in\n\u0027cgroup_shim_find\u0027. The actual cleanup of \u0027tr-\u003eprogs_hlist\u0027 in\n\u0027bpf_shim_tramp_link_release\u0027 is deferred. During this window, another\nprocess can cause a use-after-free via \u0027bpf_trampoline_link_cgroup_shim\u0027.\n\nBased on Martin KaFai Lau\u0027s suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in \u0027bpf_trampoline_link_cgroup_shim\u0027.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   \u0027bpf_shim_tramp_link_release\u0027 to make the bug easier to trigger:\n\nstatic void bpf_shim_tramp_link_release(struct bpf_link *link)\n{\n\t/* ... */\n\tif (!shim_link-\u003etrampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(\u0026shim_link-\u003elink,\n\t\tshim_link-\u003etrampoline, NULL));\n\tbpf_trampoline_put(shim_link-\u003etrampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM\u0027s report.\nAfter the patch, the bug no longer occurs even after millions of\niterations."
    }
  ],
  "id": "CVE-2026-23319",
  "lastModified": "2026-03-25T15:41:33.977",
  "metrics": {},
  "published": "2026-03-25T11:16:28.570",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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