# CVE-2026-45845: net/sched: taprio: fix NULL pointer dereference in class dump

Status: published. Published: 2026-05-27. Updated: 2026-11-06.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 665338b2a7a0139337d1f85be65ed16e487f84c1; < ec2501e361b08b50bcb1e7b3253fc861abbda28d (affected, git); ≥ 665338b2a7a0139337d1f85be65ed16e487f84c1; < d02e2fbf60de46678e2ea698a6a904fd21e1cc31 (affected, git); ≥ 665338b2a7a0139337d1f85be65ed16e487f84c1; < 48b26d48e76221dc90b02bf5428bab53643461ca (affected, git); ≥ 665338b2a7a0139337d1f85be65ed16e487f84c1; < 8f1ff8866cb9f655e5faea6994eb902960be8e04 (affected, git); ≥ 665338b2a7a0139337d1f85be65ed16e487f84c1; < 3d07ca5c0fae311226f737963984bd94bb159a87 (affected, git). Source: CNA: Linux
- Linux / Linux: 6.6 (affected); ≥ 0; < 6.6 (unaffected, semver); ≥ 6.6.141; ≤ 6.6.* (unaffected, semver); ≥ 6.12.91; ≤ 6.12.* (unaffected, semver); ≥ 6.18.33; ≤ 6.18.* (unaffected, semver); ≥ 7.0.10; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-06; percentile 1.81%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/ec2501e361b08b50bcb1e7b3253fc861abbda28d (CNA: Linux)

- https://git.kernel.org/stable/c/d02e2fbf60de46678e2ea698a6a904fd21e1cc31 (CNA: Linux)

- https://git.kernel.org/stable/c/48b26d48e76221dc90b02bf5428bab53643461ca (CNA: Linux)

- https://git.kernel.org/stable/c/8f1ff8866cb9f655e5faea6994eb902960be8e04 (CNA: Linux)

- https://git.kernel.org/stable/c/3d07ca5c0fae311226f737963984bd94bb159a87 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-45845; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-45845; retrieved 2026-11-06; source updated Not reported

Revision: e29a5d82c80e025eaa531cb65fcad2d0fbe4f38c64267e048ac563dcb1fdc363

Canonical: https://y2.dev/cve/CVE-2026-45845

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