ghsa-p7wg-mqfq-7vvc
Vulnerability from github
Published
2025-08-19 06:30
Modified
2025-08-28 15:30
Details

In the Linux kernel, the following vulnerability has been resolved:

net/sched: Restrict conditions for adding duplicating netems to qdisc tree

netem_enqueue's duplication prevention logic breaks when a netem resides in a qdisc tree with other netems - this can lead to a soft lockup and OOM loop in netem_dequeue, as seen in [1]. Ensure that a duplicating netem cannot exist in a tree with other netems.

Previous approaches suggested in discussions in chronological order:

1) Track duplication status or ttl in the sk_buff struct. Considered too specific a use case to extend such a struct, though this would be a resilient fix and address other previous and potential future DOS bugs like the one described in loopy fun [2].

2) Restrict netem_enqueue recursion depth like in act_mirred with a per cpu variable. However, netem_dequeue can call enqueue on its child, and the depth restriction could be bypassed if the child is a netem.

3) Use the same approach as in 2, but add metadata in netem_skb_cb to handle the netem_dequeue case and track a packet's involvement in duplication. This is an overly complex approach, and Jamal notes that the skb cb can be overwritten to circumvent this safeguard.

4) Prevent the addition of a netem to a qdisc tree if its ancestral path contains a netem. However, filters and actions can cause a packet to change paths when re-enqueued to the root from netem duplication, leading us to the current solution: prevent a duplicating netem from inhabiting the same tree as other netems.

[1] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/ [2] https://lwn.net/Articles/719297/

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{
  "affected": [],
  "aliases": [
    "CVE-2025-38553"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-08-19T06:15:33Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Restrict conditions for adding duplicating netems to qdisc tree\n\nnetem_enqueue\u0027s duplication prevention logic breaks when a netem\nresides in a qdisc tree with other netems - this can lead to a\nsoft lockup and OOM loop in netem_dequeue, as seen in [1].\nEnsure that a duplicating netem cannot exist in a tree with other\nnetems.\n\nPrevious approaches suggested in discussions in chronological order:\n\n1) Track duplication status or ttl in the sk_buff struct. Considered\ntoo specific a use case to extend such a struct, though this would\nbe a resilient fix and address other previous and potential future\nDOS bugs like the one described in loopy fun [2].\n\n2) Restrict netem_enqueue recursion depth like in act_mirred with a\nper cpu variable. However, netem_dequeue can call enqueue on its\nchild, and the depth restriction could be bypassed if the child is a\nnetem.\n\n3) Use the same approach as in 2, but add metadata in netem_skb_cb\nto handle the netem_dequeue case and track a packet\u0027s involvement\nin duplication. This is an overly complex approach, and Jamal\nnotes that the skb cb can be overwritten to circumvent this\nsafeguard.\n\n4) Prevent the addition of a netem to a qdisc tree if its ancestral\npath contains a netem. However, filters and actions can cause a\npacket to change paths when re-enqueued to the root from netem\nduplication, leading us to the current solution: prevent a\nduplicating netem from inhabiting the same tree as other netems.\n\n[1] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/\n[2] https://lwn.net/Articles/719297/",
  "id": "GHSA-p7wg-mqfq-7vvc",
  "modified": "2025-08-28T15:30:38Z",
  "published": "2025-08-19T06:30:26Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38553"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/09317dfb681ac5a96fc69bea0c54441cf91b8270"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/103c4e27ec9f5fe53022e46e976abf52c7221baf"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/250f8796006c0f2bc638ce545f601d49ae8d528b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/325f5ec67cc0a77f2d0d453445b9857f1cd06c76"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/795cb393e38977aa991e70a9363da0ee734b2114"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ad340a4b4adb855b18b3666f26ad65c8968e2deb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/cab2809944989889f88a1a8b5cff1c78460c72cb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ec8e0e3d7adef940cdf9475e2352c0680189d14e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f088b6ebe8797a3f948d2cae47f34bfb45cc6522"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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