veth: more robust handing of race to avoid txq getting stuck

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-68232
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-12-16 14:15:57 UTC
Updated2026-07-30 06:24:34 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: veth: more robust handing of race to avoid txq getting stuck Commit dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops") introduced a race condition that can lead to a permanently stalled TXQ. This was observed in production on ARM64 systems (Ampere Altra Max). The race occurs in veth_xmit(). The producer observes a full ptr_ring and stops the queue (netif_tx_stop_queue()). The subsequent conditional logic, intended to re-wake the queue if the consumer had just emptied it (if (__ptr_ring_empty(...)) netif_tx_wake_queue()), can fail. This leads to a "lost wakeup" where the TXQ remains stopped (QUEUE_STATE_DRV_XOFF) and traffic halts. This failure is caused by an incorrect use of the __ptr_ring_empty() API from the producer side. As noted in kernel comments, this check is not guaranteed to be correct if a consumer is operating on another CPU. The empty test is based on ptr_ring->consumer_head, making it reliable only for the consumer. Using this check from the producer side is fundamentally racy. This patch fixes the race by adopting the more robust logic from an earlier version V4 of the patchset, which always flushed the peer: (1) In veth_xmit(), the racy conditional wake-up logic and its memory barrier are removed. Instead, after stopping the queue, we unconditionally call __veth_xdp_flush(rq). This guarantees that the NAPI consumer is scheduled, making it solely responsible for re-waking the TXQ. This handles the race where veth_poll() consumes all packets and completes NAPI *before* veth_xmit() on the producer side has called netif_tx_stop_queue. The __veth_xdp_flush(rq) will observe rx_notify_masked is false and schedule NAPI. (2) On the consumer side, the logic for waking the peer TXQ is moved out of veth_xdp_rcv() and placed at the end of the veth_poll() function. This placement is part of fixing the race, as the netif_tx_queue_stopped() check must occur after rx_notify_masked is potentially set to false during NAPI completion. This handles the race where veth_poll() consumes all packets, but haven't finished (rx_notify_masked is still true). The producer veth_xmit() stops the TXQ and __veth_xdp_flush(rq) will observe rx_notify_masked is true, meaning not starting NAPI. Then veth_poll() change rx_notify_masked to false and stops NAPI. Before exiting veth_poll() will observe TXQ is stopped and wake it up.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.003480000 probability, percentile 0.274430000 (date 2026-07-31)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 9fe31b3f314534e238aa6d0b6fb492134cbcf8be dd419a3f2ebc18cc00bc32c57fd052d7a188b78b git Not specified
CNA Linux Linux affected dc82a33297fc2c58cb0b2b008d728668d45c0f6a 6c8a8b9257a660e622689e23c8fbad4ba2b561b9 git Not specified
CNA Linux Linux affected dc82a33297fc2c58cb0b2b008d728668d45c0f6a 5442a9da69789741bfda39f34ee7f69552bf0c56 git Not specified
CNA Linux Linux affected 6.16 Not specified
CNA Linux Linux unaffected 6.16 semver Not specified
CNA Linux Linux unaffected 6.17.10 6.17.* semver Not specified
CNA Linux Linux unaffected 6.18 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/dd419a3f2ebc18cc00bc32c57fd052d7a188b78b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6c8a8b9257a660e622689e23c8fbad4ba2b561b9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5442a9da69789741bfda39f34ee7f69552bf0c56 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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