veth: fix queue index used to wake the peer txq in veth_poll
veth_poll() derives the index of the peer TX queue to wake from
rq->xdp_rxq.queue_index. That field is only initialized by
xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an
XDP program is attached. On the plain GRO/NAPI path
(veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so
queue_index stays 0 for every queue, as priv->rq is zero-allocated.
So in a multi-queue setup with GRO enabled and no XDP program attached,
every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops
peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing
ever wakes it again: the poller draining queue 1 wakes queue 0 instead.
veth implements no ndo_tx_timeout, so the netdev watchdog does not kick
in either, and the queue stays stopped indefinitely.
Derive the index from the position of the rq within priv->rq instead,
which is correct regardless of whether XDP was ever enabled.
Scripts to reproduce the stall are available at
https://github.com/netoptimizer/veth-backpressure-performance-testing
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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Wed, 26 Aug 2026 14:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: veth: fix queue index used to wake the peer txq in veth_poll veth_poll() derives the index of the peer TX queue to wake from rq->xdp_rxq.queue_index. That field is only initialized by xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an XDP program is attached. On the plain GRO/NAPI path (veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so queue_index stays 0 for every queue, as priv->rq is zero-allocated. So in a multi-queue setup with GRO enabled and no XDP program attached, every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing ever wakes it again: the poller draining queue 1 wakes queue 0 instead. veth implements no ndo_tx_timeout, so the netdev watchdog does not kick in either, and the queue stays stopped indefinitely. Derive the index from the position of the rq within priv->rq instead, which is correct regardless of whether XDP was ever enabled. Scripts to reproduce the stall are available at https://github.com/netoptimizer/veth-backpressure-performance-testing | |
| Title | veth: fix queue index used to wake the peer txq in veth_poll | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-08-26T14:36:53.580Z
Reserved: 2026-08-15T05:44:03.930Z
Link: CVE-2026-74742
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-26T15:16:52.990
Modified: 2026-08-26T15:16:52.990
Link: CVE-2026-74742
Redhat
No data.
OpenCVE Enrichment
No data.
No weakness.