CVE-2025-21702 (GCVE-0-2025-21702)

Vulnerability from cvelistv5 – Published: 2025-02-18 14:37 – Updated: 2025-11-03 19:35
VLAI?
Title
pfifo_tail_enqueue: Drop new packet when sch->limit == 0
Summary
In the Linux kernel, the following vulnerability has been resolved: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. - Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < 78285b53266d6d51fa4ff504a23df03852eba84e (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < 7a9723ec27aff5674f1fd4934608937f1d650980 (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < a56a6e8589a9b98d8171611fbcc1e45a15fd2455 (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < 020ecb76812a0526f4130ab5aeb6dc7c773e7ab9 (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < 79a955ea4a2e5ddf4a36328959de0de496419888 (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < e40cb34b7f247fe2e366fd192700d1b4f38196ca (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < b6a079c3b6f95378f26e2aeda520cb3176f7067b (git)
Affected: 57dbb2d83d100ea601c54fe129bfde0678db5dee , < 647cef20e649c576dff271e018d5d15d998b629d (git)
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    Linux Linux Affected: 2.6.34
Unaffected: 0 , < 2.6.34 (semver)
Unaffected: 5.4.291 , ≤ 5.4.* (semver)
Unaffected: 5.10.235 , ≤ 5.10.* (semver)
Unaffected: 5.15.179 , ≤ 5.15.* (semver)
Unaffected: 6.1.130 , ≤ 6.1.* (semver)
Unaffected: 6.6.83 , ≤ 6.6.* (semver)
Unaffected: 6.12.14 , ≤ 6.12.* (semver)
Unaffected: 6.13.3 , ≤ 6.13.* (semver)
Unaffected: 6.14 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\npfifo_tail_enqueue: Drop new packet when sch-\u003elimit == 0\n\nExpected behaviour:\nIn case we reach scheduler\u0027s limit, pfifo_tail_enqueue() will drop a\npacket in scheduler\u0027s queue and decrease scheduler\u0027s qlen by one.\nThen, pfifo_tail_enqueue() enqueue new packet and increase\nscheduler\u0027s qlen by one. Finally, pfifo_tail_enqueue() return\n`NET_XMIT_CN` status code.\n\nWeird behaviour:\nIn case we set `sch-\u003elimit == 0` and trigger pfifo_tail_enqueue() on a\nscheduler that has no packet, the \u0027drop a packet\u0027 step will do nothing.\nThis means the scheduler\u0027s qlen still has value equal 0.\nThen, we continue to enqueue new packet and increase scheduler\u0027s qlen by\none. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by\none and return `NET_XMIT_CN` status code.\n\nThe problem is:\nLet\u0027s say we have two qdiscs: Qdisc_A and Qdisc_B.\n - Qdisc_A\u0027s type must have \u0027-\u003egraft()\u0027 function to create parent/child relationship.\n   Let\u0027s say Qdisc_A\u0027s type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`.\n - Qdisc_B\u0027s type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`.\n - Qdisc_B is configured to have `sch-\u003elimit == 0`.\n - Qdisc_A is configured to route the enqueued\u0027s packet to Qdisc_B.\n\nEnqueue packet through Qdisc_A will lead to:\n - hfsc_enqueue(Qdisc_A) -\u003e pfifo_tail_enqueue(Qdisc_B)\n - Qdisc_B-\u003eq.qlen += 1\n - pfifo_tail_enqueue() return `NET_XMIT_CN`\n - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` =\u003e hfsc_enqueue() don\u0027t increase qlen of Qdisc_A.\n\nThe whole process lead to a situation where Qdisc_A-\u003eq.qlen == 0 and Qdisc_B-\u003eq.qlen == 1.\nReplace \u0027hfsc\u0027 with other type (for example: \u0027drr\u0027) still lead to the same problem.\nThis violate the design where parent\u0027s qlen should equal to the sum of its childrens\u0027qlen.\n\nBug impact: This issue can be used for user-\u003ekernel privilege escalation when it is reachable."
        }
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/78285b53266d6d51fa4ff504a23df03852eba84e"
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          "url": "https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980"
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          "url": "https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9"
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      "title": "pfifo_tail_enqueue: Drop new packet when sch-\u003elimit == 0",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21702",
    "datePublished": "2025-02-18T14:37:43.429Z",
    "dateReserved": "2024-12-29T08:45:45.748Z",
    "dateUpdated": "2025-11-03T19:35:50.649Z",
    "state": "PUBLISHED"
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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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