CVE-2026-23340

Description

In the Linux kernel, the following vulnerability has been resolved:net: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscsWhen shrinking the number of real tx queues,netif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flushqdiscs for queues which will no longer be used.qdisc_reset_all_tx_gt() currently serializes qdisc_reset() withqdisc_lock(). However, for lockless qdiscs, the dequeue path isserialized by qdisc_run_begin/end() using qdisc->seqlock instead, soqdisc_reset() can run concurrently with __qdisc_run() and free skbswhile they are still being dequeued, leading to UAF.This can easily be reproduced on e.g. virtio-net by imposing heavytraffic 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 doneWith KASAN enabled, this leads to reports like: BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760 ... Call Trace: ... __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 ... 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 bytaking qdisc->seqlock for TCQ_F_NOLOCK qdiscs, matching theserialization model already used by dev_reset_queue().Additionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc statereflects an empty queue, avoiding needless re-scheduling.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234