CVE-2026-23340High· 7.8▾ TwilightIn 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_r…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 42.9 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
Last analysed / modified upstream
0.1%
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.
Linux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < 5bb27ad54d12de67e457d7d251198e361bef835eLinux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < 7594467c49bfc2f4644dee0415ac2290db11fa0dLinux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < dbd58b0730aa06ab6ad26079cf9a5b6b58e7e750Linux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < 5bc4e69306ed7ae02232eb4c0b23ed621a26d504Linux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < 8314944cc3bdeaa5a73e6f8a8cf0d94822e625cbLinux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < c69df4e0524f8de8e176ba389acd83e85f5f49d0Linux >= 6b3ba9146fe64b9bebb6346c9dcfe3b4851de2d7 < 7f083faf59d14c04e01ec05a7507f036c965acf8Linux 4.16Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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