{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21884",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21884"
  ],
  "published": "2025-03-27T15:01:31Z",
  "summary": "net: better track kernel sockets lifetime",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: better track kernel sockets lifetime\n\nWhile kernel sockets are dismantled during pernet_operations->exit(),\ntheir freeing can be delayed by any tx packets still held in qdisc\nor device queues, due to skb_set_owner_w() prior calls.\n\nThis then trigger the following warning from ref_tracker_dir_exit() [1]\n\nTo fix this, make sure that kernel sockets own a reference on net->passive.\n\nAdd sk_net_refcnt_upgrade() helper, used whenever a kernel socket\nis converted to a refcounted one.\n\n[1]\n\n[  136.263918][   T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at\n[  136.263918][   T35]      sk_alloc+0x2b3/0x370\n[  136.263918][   T35]      inet6_create+0x6ce/0x10f0\n[  136.263918][   T35]      __sock_create+0x4c0/0xa30\n[  136.263918][   T35]      inet_ctl_sock_create+0xc2/0x250\n[  136.263918][   T35]      igmp6_net_init+0x39/0x390\n[  136.263918][   T35]      ops_init+0x31e/0x590\n[  136.263918][   T35]      setup_net+0x287/0x9e0\n[  136.263918][   T35]      copy_net_ns+0x33f/0x570\n[  136.263918][   T35]      create_new_namespaces+0x425/0x7b0\n[  136.263918][   T35]      unshare_nsproxy_namespaces+0x124/0x180\n[  136.263918][   T35]      ksys_unshare+0x57d/0xa70\n[  136.263918][   T35]      __x64_sys_unshare+0x38/0x40\n[  136.263918][   T35]      do_syscall_64+0xf3/0x230\n[  136.263918][   T35]      entry_SYSCALL_64_after_hwframe+0x77/0x7f\n[  136.263918][   T35]\n[  136.343488][   T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at\n[  136.343488][   T35]      sk_alloc+0x2b3/0x370\n[  136.343488][   T35]      inet6_create+0x6ce/0x10f0\n[  136.343488][   T35]      __sock_create+0x4c0/0xa30\n[  136.343488][   T35]      inet_ctl_sock_create+0xc2/0x250\n[  136.343488][   T35]      ndisc_net_init+0xa7/0x2b0\n[  136.343488][   T35]      ops_init+0x31e/0x590\n[  136.343488][   T35]      setup_net+0x287/0x9e0\n[  136.343488][   T35]      copy_net_ns+0x33f/0x570\n[  136.343488][   T35]      create_new_namespaces+0x425/0x7b0\n[  136.343488][   T35]      unshare_nsproxy_namespaces+0x124/0x180\n[  136.343488][   T35]      ksys_unshare+0x57d/0xa70\n[  136.343488][   T35]      __x64_sys_unshare+0x38/0x40\n[  136.343488][   T35]      do_syscall_64+0xf3/0x230\n[  136.343488][   T35]      entry_SYSCALL_64_after_hwframe+0x77/0x7f",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
  "affected": [
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            "binary_name": "linux-image-6.12.34+rpt-rpi-v8-rt",
            "binary_version": "1:6.12.34-1+rpt1"
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      "database_specific": {
        "per_version": {
          "1:6.12.19-1+rpt1~bpo12+1": {
            "linux_commit": "121c2c384b9c2f4790ffb31b2cd25c7d75c8fda0",
            "upstream_version": "6.12.19",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.43"
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            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.43"
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            "assessment": "commit ancestry (strak rule)",
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            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.43"
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    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-21884"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/2668e038800b946d269f96ec1b258c01930a242c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4ceb0bd4ffd009821b585ce6a8033b12b59fb5fb"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c31a732fac46b00b95b78fcc9c37cb48dd6f2e0c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/5c70eb5c593d64d93b178905da215a9fd288a4b5"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The bug is triggered entirely through local syscalls \u2014 `unshare(CLONE_NEWUSER|CLONE_NEWNET)` to create the netns, netlink/rtnetlink to add a device and a delaying qdisc, then namespace exit to run `cleanup_net()`; the syzbot traces show the path rooted at `__x64_sys_unshare`. No remote peer input is required or sufficient to reach it.\nAC:L - The attacker controls both halves of the window: they configure the device/qdisc that holds the kernel socket's TX skb (e.g. netem delay) and they choose exactly when to destroy the namespace, so the socket reliably outlives `net_passive_dec()`; the syzkaller reproducer hit it repeatably. Namespace churn also lets the attacker groom the freed `net_cachep` object before the deferred `__sk_destruct()` runs.\nPR:L - An unprivileged local account can create the network namespace and its per-netns kernel sockets via unprivileged user namespaces (`unshare -Urn`), which is enabled by default on mainstream distributions and Android. CAP_NET_ADMIN inside the new netns \u2014 granted automatically \u2014 is enough to add the device and qdisc needed to delay the kernel socket's skbs.\nUI:N - The attacking process performs every step itself: create the namespace, configure the delaying queue, trigger MLD/NDISC transmission, and exit. No victim action or cooperating process is needed.\nS:U - The freed `struct net`/`net->gen` slab objects and the sockets that dereference them all live in the kernel's own security authority. No hypervisor, IOMMU, or sandbox boundary is crossed, so this is standard in-kernel corruption.\nC:H - The kernel socket retains a completely unreferenced `struct net *`, so after `net_passive_dec()` frees `net->gen` and returns the `struct net` to `net_cachep`, subsequent `sock_net(sk)` dereferences read reallocated slab contents \u2014 the same class of defect that produced a KASAN slab-use-after-free read in the companion commit `65161fb544aa`. A use-after-free on a long-lived, attacker-groomable object yields an information-disclosure primitive.\nI:H - `__sk_destruct()` performs `__netns_tracker_free(sock_net(sk), &sk->ns_tracker, false)` on the dangling pointer, driving `ref_tracker_free()`'s list unlink and counter updates into the freed-and-reallocated `struct net`, which is a write into attacker-groomed memory. Reallocating the freed slot with a fresh namespace also lets the stale socket operate on the wrong `struct net`, corrupting per-netns state and enabling escalation to control-flow hijack.\nA:H - Use-after-free of `struct net` and its freed `net->gen` array produces oopses and panics even when not weaponized, and the pre-fix condition additionally trips `ref_tracker_dir_exit()`'s WARN with `CONFIG_NET_NS_REFCNT_TRACKER=y` (fatal under `panic_on_warn`). The sequence can be repeated in a loop by an unprivileged user until the box crashes."
    }
  }
}