FKIE_CVE-2026-45845

Vulnerability from fkie_nvd - Published: 2026-05-27 11:16 - Updated: 2026-05-27 14:48
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: taprio: fix NULL pointer dereference in class dump When a TAPRIO child qdisc is deleted via RTM_DELQDISC, taprio_graft() is called with new == NULL and stores NULL into q->qdiscs[cl - 1]. Subsequent RTM_GETTCLASS dump operations walk all classes via taprio_walk() and call taprio_dump_class(), which calls taprio_leaf() returning the NULL pointer, then dereferences it to read child->handle, causing a kernel NULL pointer dereference. The bug is reachable with namespace-scoped CAP_NET_ADMIN on any kernel with CONFIG_NET_SCH_TAPRIO enabled. On systems with unprivileged user namespaces enabled, an unprivileged local user can trigger a kernel panic by creating a taprio qdisc inside a new network namespace, grafting an explicit child qdisc, deleting it, and requesting a class dump. The RTM_GETTCLASS dump itself requires no capability. Oops: general protection fault, probably for non-canonical address 0xdffffc0000000007: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:taprio_dump_class (net/sched/sch_taprio.c:2478) Call Trace: <TASK> tc_fill_tclass (net/sched/sch_api.c:1966) qdisc_class_dump (net/sched/sch_api.c:2326) taprio_walk (net/sched/sch_taprio.c:2514) tc_dump_tclass_qdisc (net/sched/sch_api.c:2352) tc_dump_tclass_root (net/sched/sch_api.c:2370) tc_dump_tclass (net/sched/sch_api.c:2431) rtnl_dumpit (net/core/rtnetlink.c:6864) netlink_dump (net/netlink/af_netlink.c:2325) rtnetlink_rcv_msg (net/core/rtnetlink.c:6959) netlink_rcv_skb (net/netlink/af_netlink.c:2550) </TASK> Fix this by substituting &noop_qdisc when new is NULL in taprio_graft(), a common pattern used by other qdiscs (e.g., multiq_graft()) to ensure the q->qdiscs[] slots are never NULL. This makes control-plane dump paths safe without requiring individual NULL checks. Since the data-plane paths (taprio_enqueue and taprio_dequeue_from_txq) previously had explicit NULL guards that would drop/skip the packet cleanly, update those checks to test for &noop_qdisc instead. Without this, packets would reach taprio_enqueue_one() which increments the root qdisc's qlen and backlog before calling the child's enqueue; noop_qdisc drops the packet but those counters are never rolled back, permanently inflating the root qdisc's statistics. After this change *old can be a valid qdisc, NULL, or &noop_qdisc. Only call qdisc_put(*old) in the first case to avoid decreasing noop_qdisc's refcount, which was never increased.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3d07ca5c0fae311226f737963984bd94bb159a87
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/48b26d48e76221dc90b02bf5428bab53643461ca
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8f1ff8866cb9f655e5faea6994eb902960be8e04
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d02e2fbf60de46678e2ea698a6a904fd21e1cc31
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ec2501e361b08b50bcb1e7b3253fc861abbda28d
Impacted products
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: taprio: fix NULL pointer dereference in class dump\n\nWhen a TAPRIO child qdisc is deleted via RTM_DELQDISC, taprio_graft()\nis called with new == NULL and stores NULL into q-\u003eqdiscs[cl - 1].\nSubsequent RTM_GETTCLASS dump operations walk all classes via\ntaprio_walk() and call taprio_dump_class(), which calls taprio_leaf()\nreturning the NULL pointer, then dereferences it to read child-\u003ehandle,\ncausing a kernel NULL pointer dereference.\n\nThe bug is reachable with namespace-scoped CAP_NET_ADMIN on any kernel\nwith CONFIG_NET_SCH_TAPRIO enabled. On systems with unprivileged user\nnamespaces enabled, an unprivileged local user can trigger a kernel\npanic by creating a taprio qdisc inside a new network namespace,\ngrafting an explicit child qdisc, deleting it, and requesting a class\ndump. The RTM_GETTCLASS dump itself requires no capability.\n\n Oops: general protection fault, probably for non-canonical address 0xdffffc0000000007: 0000 [#1] SMP KASAN NOPTI\n KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]\n RIP: 0010:taprio_dump_class (net/sched/sch_taprio.c:2478)\n Call Trace:\n  \u003cTASK\u003e\n  tc_fill_tclass (net/sched/sch_api.c:1966)\n  qdisc_class_dump (net/sched/sch_api.c:2326)\n  taprio_walk (net/sched/sch_taprio.c:2514)\n  tc_dump_tclass_qdisc (net/sched/sch_api.c:2352)\n  tc_dump_tclass_root (net/sched/sch_api.c:2370)\n  tc_dump_tclass (net/sched/sch_api.c:2431)\n  rtnl_dumpit (net/core/rtnetlink.c:6864)\n  netlink_dump (net/netlink/af_netlink.c:2325)\n  rtnetlink_rcv_msg (net/core/rtnetlink.c:6959)\n  netlink_rcv_skb (net/netlink/af_netlink.c:2550)\n  \u003c/TASK\u003e\n\nFix this by substituting \u0026noop_qdisc when new is NULL in\ntaprio_graft(), a common pattern used by other qdiscs (e.g.,\nmultiq_graft()) to ensure the q-\u003eqdiscs[] slots are never NULL.\nThis makes control-plane dump paths safe without requiring individual\nNULL checks.\n\nSince the data-plane paths (taprio_enqueue and taprio_dequeue_from_txq)\npreviously had explicit NULL guards that would drop/skip the packet\ncleanly, update those checks to test for \u0026noop_qdisc instead. Without\nthis, packets would reach taprio_enqueue_one() which increments the root\nqdisc\u0027s qlen and backlog before calling the child\u0027s enqueue; noop_qdisc\ndrops the packet but those counters are never rolled back, permanently\ninflating the root qdisc\u0027s statistics.\n\nAfter this change *old can be a valid qdisc, NULL, or \u0026noop_qdisc.\nOnly call qdisc_put(*old) in the first case to avoid decreasing\nnoop_qdisc\u0027s refcount, which was never increased."
    }
  ],
  "id": "CVE-2026-45845",
  "lastModified": "2026-05-27T14:48:31.480",
  "metrics": {},
  "published": "2026-05-27T11:16:23.960",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3d07ca5c0fae311226f737963984bd94bb159a87"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/48b26d48e76221dc90b02bf5428bab53643461ca"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/8f1ff8866cb9f655e5faea6994eb902960be8e04"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d02e2fbf60de46678e2ea698a6a904fd21e1cc31"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ec2501e361b08b50bcb1e7b3253fc861abbda28d"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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