CVE-2025-38553 (GCVE-0-2025-38553)

Vulnerability from cvelistv5 – Published: 2025-08-19 06:06 – Updated: 2025-11-03 17:39
VLAI?
Title
net/sched: Restrict conditions for adding duplicating netems to qdisc tree
Summary
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/
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < ad340a4b4adb855b18b3666f26ad65c8968e2deb (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < f088b6ebe8797a3f948d2cae47f34bfb45cc6522 (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < cab2809944989889f88a1a8b5cff1c78460c72cb (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < 325f5ec67cc0a77f2d0d453445b9857f1cd06c76 (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < 103c4e27ec9f5fe53022e46e976abf52c7221baf (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < 795cb393e38977aa991e70a9363da0ee734b2114 (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < 250f8796006c0f2bc638ce545f601d49ae8d528b (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < 09317dfb681ac5a96fc69bea0c54441cf91b8270 (git)
Affected: 0afb51e72855971dba83b3c6b70c547c2d1161fd , < ec8e0e3d7adef940cdf9475e2352c0680189d14e (git)
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    Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 5.4.297 , ≤ 5.4.* (semver)
Unaffected: 5.10.241 , ≤ 5.10.* (semver)
Unaffected: 5.15.190 , ≤ 5.15.* (semver)
Unaffected: 6.1.148 , ≤ 6.1.* (semver)
Unaffected: 6.6.102 , ≤ 6.6.* (semver)
Unaffected: 6.12.42 , ≤ 6.12.* (semver)
Unaffected: 6.15.10 , ≤ 6.15.* (semver)
Unaffected: 6.16.1 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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          "value": "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/"
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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • 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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