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CVE-2026-23340

net: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscs

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.203, 6.1.167, 6.6.130, 6.12.77, 6.18.17, and 1 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

In the Linux kernel, the following vulnerability has been resolved: net: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscs When shrinking the number of real tx queues, netif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flush qdiscs for queues which will no longer be used. qdisc_reset_all_tx_gt() currently serializes qdisc_reset() with qdisc_lock(). However, for lockless qdiscs, the dequeue path is serialized by qdisc_run_begin/end() using qdisc->seqlock instead, so qdisc_reset() can run concurrently with __qdisc_run() and free skbs while they are still being dequeued, leading to UAF. This can easily be reproduced on e.g. virtio-net by imposing heavy traffic while frequently changing the number of queue pairs: iperf3 -ub0 -c $peer -t 0 & while :; do ethtool -L eth0 combined 1 ethtool -L eth0 combined 2 done With KASAN enabled, this leads to reports like: BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760 ... Call Trace: <TASK> ... __qdisc_run+0x133f/0x1760 __dev_queue_xmit+0x248f/0x3550 ip_finish_output2+0xa42/0x2110 ip_output+0x1a7/0x410 ip_send_skb+0x2e6/0x480 udp_send_skb+0xb0a/0x1590 udp_sendmsg+0x13c9/0x1fc0 ... </TASK> Allocated by task 1270 on cpu 5 at 44.558414s: ... alloc_skb_with_frags+0x84/0x7c0 sock_alloc_send_pskb+0x69a/0x830 __ip_append_data+0x1b86/0x48c0 ip_make_skb+0x1e8/0x2b0 udp_sendmsg+0x13a6/0x1fc0 ... Freed by task 1306 on cpu 3 at 44.558445s: ... kmem_cache_free+0x117/0x5e0 pfifo_fast_reset+0x14d/0x580 qdisc_reset+0x9e/0x5f0 netif_set_real_num_tx_queues+0x303/0x840 virtnet_set_channels+0x1bf/0x260 [virtio_net] ethnl_set_channels+0x684/0xae0 ethnl_default_set_doit+0x31a/0x890 ... Serialize qdisc_reset_all_tx_gt() against the lockless dequeue path by taking qdisc->seqlock for TCQ_F_NOLOCK qdiscs, matching the serialization model already used by dev_reset_queue(). Additionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc state reflects an empty queue, avoiding needless re-scheduling.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in 5bb27ad54d12de67e457d7d251198e361bef835e; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in 7594467c49bfc2f4644dee0415ac2290db11fa0d; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in dbd58b0730aa06ab6ad26079cf9a5b6b58e7e750; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in 5bc4e69306ed7ae02232eb4c0b23ed621a26d504; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in 8314944cc3bdeaa5a73e6f8a8cf0d94822e625cb; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in c69df4e0524f8de8e176ba389acd83e85f5f49d0; From 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 · fixed in 7f083faf59d14c04e01ec05a7507f036c965acf8

  • Linux Linux

    4.16

  • KernelLinux

    From 4.16.0 · fixed in 5.15.203; From 5.16.0 · fixed in 6.1.167; From 6.2.0 · fixed in 6.6.130; From 6.7.0 · fixed in 6.12.77; From 6.13.0 · fixed in 6.18.17; From 6.19.0 · fixed in 6.19.7

References 7

git.kernel.org