GHSA-27RJ-CHMQ-RH6R
Vulnerability from github – Published: 2026-03-25 12:30 – Updated: 2026-07-14 15:31In 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: ... __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 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.
{
"affected": [],
"aliases": [
"CVE-2026-23340"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-03-25T11:16:31Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscs\n\nWhen shrinking the number of real tx queues,\nnetif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flush\nqdiscs for queues which will no longer be used.\n\nqdisc_reset_all_tx_gt() currently serializes qdisc_reset() with\nqdisc_lock(). However, for lockless qdiscs, the dequeue path is\nserialized by qdisc_run_begin/end() using qdisc-\u003eseqlock instead, so\nqdisc_reset() can run concurrently with __qdisc_run() and free skbs\nwhile they are still being dequeued, leading to UAF.\n\nThis can easily be reproduced on e.g. virtio-net by imposing heavy\ntraffic while frequently changing the number of queue pairs:\n\n iperf3 -ub0 -c $peer -t 0 \u0026\n while :; do\n ethtool -L eth0 combined 1\n ethtool -L eth0 combined 2\n done\n\nWith KASAN enabled, this leads to reports like:\n\n BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760\n ...\n Call Trace:\n \u003cTASK\u003e\n ...\n __qdisc_run+0x133f/0x1760\n __dev_queue_xmit+0x248f/0x3550\n ip_finish_output2+0xa42/0x2110\n ip_output+0x1a7/0x410\n ip_send_skb+0x2e6/0x480\n udp_send_skb+0xb0a/0x1590\n udp_sendmsg+0x13c9/0x1fc0\n ...\n \u003c/TASK\u003e\n\n Allocated by task 1270 on cpu 5 at 44.558414s:\n ...\n alloc_skb_with_frags+0x84/0x7c0\n sock_alloc_send_pskb+0x69a/0x830\n __ip_append_data+0x1b86/0x48c0\n ip_make_skb+0x1e8/0x2b0\n udp_sendmsg+0x13a6/0x1fc0\n ...\n\n Freed by task 1306 on cpu 3 at 44.558445s:\n ...\n kmem_cache_free+0x117/0x5e0\n pfifo_fast_reset+0x14d/0x580\n qdisc_reset+0x9e/0x5f0\n netif_set_real_num_tx_queues+0x303/0x840\n virtnet_set_channels+0x1bf/0x260 [virtio_net]\n ethnl_set_channels+0x684/0xae0\n ethnl_default_set_doit+0x31a/0x890\n ...\n\nSerialize qdisc_reset_all_tx_gt() against the lockless dequeue path by\ntaking qdisc-\u003eseqlock for TCQ_F_NOLOCK qdiscs, matching the\nserialization model already used by dev_reset_queue().\n\nAdditionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc state\nreflects an empty queue, avoiding needless re-scheduling.",
"id": "GHSA-27rj-chmq-rh6r",
"modified": "2026-07-14T15:31:41Z",
"published": "2026-03-25T12:30:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23340"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5bb27ad54d12de67e457d7d251198e361bef835e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5bc4e69306ed7ae02232eb4c0b23ed621a26d504"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7594467c49bfc2f4644dee0415ac2290db11fa0d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7f083faf59d14c04e01ec05a7507f036c965acf8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8314944cc3bdeaa5a73e6f8a8cf0d94822e625cb"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c69df4e0524f8de8e176ba389acd83e85f5f49d0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dbd58b0730aa06ab6ad26079cf9a5b6b58e7e750"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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