CVE-2025-38553

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/

Affected Software

VendorProductVersion RangeStatus
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < ad340a4b4adb855b18b3666f26ad65c8968e2debaffected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < f088b6ebe8797a3f948d2cae47f34bfb45cc6522affected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < cab2809944989889f88a1a8b5cff1c78460c72cbaffected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < 325f5ec67cc0a77f2d0d453445b9857f1cd06c76affected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < 103c4e27ec9f5fe53022e46e976abf52c7221bafaffected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < 795cb393e38977aa991e70a9363da0ee734b2114affected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < 250f8796006c0f2bc638ce545f601d49ae8d528baffected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < 09317dfb681ac5a96fc69bea0c54441cf91b8270affected
LinuxLinux0afb51e72855971dba83b3c6b70c547c2d1161fd < ec8e0e3d7adef940cdf9475e2352c0680189d14eaffected
LinuxLinux2.6.12affected
LinuxLinux0 < 2.6.12unaffected
LinuxLinux5.4.297 <= 5.4.*unaffected
LinuxLinux5.10.241 <= 5.10.*unaffected
LinuxLinux5.15.190 <= 5.15.*unaffected
LinuxLinux6.1.148 <= 6.1.*unaffected
LinuxLinux6.6.102 <= 6.6.*unaffected
LinuxLinux6.12.42 <= 6.12.*unaffected
LinuxLinux6.15.10 <= 6.15.*unaffected
LinuxLinux6.16.1 <= 6.16.*unaffected
LinuxLinux6.17 <= *unaffected

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

References