CVE-2025-68232 (GCVE-0-2025-68232)

Vulnerability from cvelistv5 – Published: 2025-12-16 14:04 – Updated: 2025-12-16 14:04
VLAI?
Title
veth: more robust handing of race to avoid txq getting stuck
Summary
In 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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 9fe31b3f314534e238aa6d0b6fb492134cbcf8be , < dd419a3f2ebc18cc00bc32c57fd052d7a188b78b (git)
Affected: dc82a33297fc2c58cb0b2b008d728668d45c0f6a , < 6c8a8b9257a660e622689e23c8fbad4ba2b561b9 (git)
Affected: dc82a33297fc2c58cb0b2b008d728668d45c0f6a , < 5442a9da69789741bfda39f34ee7f69552bf0c56 (git)
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    Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.17.10 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/veth.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nveth: more robust handing of race to avoid txq getting stuck\n\nCommit dc82a33297fc (\"veth: apply qdisc backpressure on full ptr_ring to\nreduce TX drops\") introduced a race condition that can lead to a permanently\nstalled TXQ. This was observed in production on ARM64 systems (Ampere Altra\nMax).\n\nThe race occurs in veth_xmit(). The producer observes a full ptr_ring and\nstops the queue (netif_tx_stop_queue()). The subsequent conditional logic,\nintended to re-wake the queue if the consumer had just emptied it (if\n(__ptr_ring_empty(...)) netif_tx_wake_queue()), can fail. This leads to a\n\"lost wakeup\" where the TXQ remains stopped (QUEUE_STATE_DRV_XOFF) and\ntraffic halts.\n\nThis failure is caused by an incorrect use of the __ptr_ring_empty() API\nfrom the producer side. As noted in kernel comments, this check is not\nguaranteed to be correct if a consumer is operating on another CPU. The\nempty test is based on ptr_ring-\u003econsumer_head, making it reliable only for\nthe consumer. Using this check from the producer side is fundamentally racy.\n\nThis patch fixes the race by adopting the more robust logic from an earlier\nversion V4 of the patchset, which always flushed the peer:\n\n(1) In veth_xmit(), the racy conditional wake-up logic and its memory barrier\nare removed. Instead, after stopping the queue, we unconditionally call\n__veth_xdp_flush(rq). This guarantees that the NAPI consumer is scheduled,\nmaking it solely responsible for re-waking the TXQ.\n  This handles the race where veth_poll() consumes all packets and completes\nNAPI *before* veth_xmit() on the producer side has called netif_tx_stop_queue.\nThe __veth_xdp_flush(rq) will observe rx_notify_masked is false and schedule\nNAPI.\n\n(2) On the consumer side, the logic for waking the peer TXQ is moved out of\nveth_xdp_rcv() and placed at the end of the veth_poll() function. This\nplacement is part of fixing the race, as the netif_tx_queue_stopped() check\nmust occur after rx_notify_masked is potentially set to false during NAPI\ncompletion.\n  This handles the race where veth_poll() consumes all packets, but haven\u0027t\nfinished (rx_notify_masked is still true). The producer veth_xmit() stops the\nTXQ and __veth_xdp_flush(rq) will observe rx_notify_masked is true, meaning\nnot starting NAPI.  Then veth_poll() change rx_notify_masked to false and\nstops NAPI.  Before exiting veth_poll() will observe TXQ is stopped and wake\nit up."
        }
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        "dateUpdated": "2025-12-16T14:04:12.624Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/dd419a3f2ebc18cc00bc32c57fd052d7a188b78b"
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          "url": "https://git.kernel.org/stable/c/6c8a8b9257a660e622689e23c8fbad4ba2b561b9"
        },
        {
          "url": "https://git.kernel.org/stable/c/5442a9da69789741bfda39f34ee7f69552bf0c56"
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      "title": "veth: more robust handing of race to avoid txq getting stuck",
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    "cveId": "CVE-2025-68232",
    "datePublished": "2025-12-16T14:04:12.624Z",
    "dateReserved": "2025-12-16T13:41:40.258Z",
    "dateUpdated": "2025-12-16T14:04:12.624Z",
    "state": "PUBLISHED"
  },
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    "nvd": "{\"cve\":{\"id\":\"CVE-2025-68232\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-12-16T14:15:57.633\",\"lastModified\":\"2025-12-18T15:08:06.237\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nveth: more robust handing of race to avoid txq getting stuck\\n\\nCommit dc82a33297fc (\\\"veth: apply qdisc backpressure on full ptr_ring to\\nreduce TX drops\\\") introduced a race condition that can lead to a permanently\\nstalled TXQ. This was observed in production on ARM64 systems (Ampere Altra\\nMax).\\n\\nThe race occurs in veth_xmit(). The producer observes a full ptr_ring and\\nstops the queue (netif_tx_stop_queue()). The subsequent conditional logic,\\nintended to re-wake the queue if the consumer had just emptied it (if\\n(__ptr_ring_empty(...)) netif_tx_wake_queue()), can fail. This leads to a\\n\\\"lost wakeup\\\" where the TXQ remains stopped (QUEUE_STATE_DRV_XOFF) and\\ntraffic halts.\\n\\nThis failure is caused by an incorrect use of the __ptr_ring_empty() API\\nfrom the producer side. As noted in kernel comments, this check is not\\nguaranteed to be correct if a consumer is operating on another CPU. The\\nempty test is based on ptr_ring-\u003econsumer_head, making it reliable only for\\nthe consumer. Using this check from the producer side is fundamentally racy.\\n\\nThis patch fixes the race by adopting the more robust logic from an earlier\\nversion V4 of the patchset, which always flushed the peer:\\n\\n(1) In veth_xmit(), the racy conditional wake-up logic and its memory barrier\\nare removed. Instead, after stopping the queue, we unconditionally call\\n__veth_xdp_flush(rq). This guarantees that the NAPI consumer is scheduled,\\nmaking it solely responsible for re-waking the TXQ.\\n  This handles the race where veth_poll() consumes all packets and completes\\nNAPI *before* veth_xmit() on the producer side has called netif_tx_stop_queue.\\nThe __veth_xdp_flush(rq) will observe rx_notify_masked is false and schedule\\nNAPI.\\n\\n(2) On the consumer side, the logic for waking the peer TXQ is moved out of\\nveth_xdp_rcv() and placed at the end of the veth_poll() function. This\\nplacement is part of fixing the race, as the netif_tx_queue_stopped() check\\nmust occur after rx_notify_masked is potentially set to false during NAPI\\ncompletion.\\n  This handles the race where veth_poll() consumes all packets, but haven\u0027t\\nfinished (rx_notify_masked is still true). The producer veth_xmit() stops the\\nTXQ and __veth_xdp_flush(rq) will observe rx_notify_masked is true, meaning\\nnot starting NAPI.  Then veth_poll() change rx_notify_masked to false and\\nstops NAPI.  Before exiting veth_poll() will observe TXQ is stopped and wake\\nit up.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/5442a9da69789741bfda39f34ee7f69552bf0c56\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/6c8a8b9257a660e622689e23c8fbad4ba2b561b9\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/dd419a3f2ebc18cc00bc32c57fd052d7a188b78b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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