CVE-2025-38637

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

net_sched: skbprio: Remove overly strict queue assertions

In the current implementation, skbprio enqueue/dequeue contains an assertion that fails under certain conditions when SKBPRIO is used as a child qdisc under TBF with specific parameters. The failure occurs because TBF sometimes peeks at packets in the child qdisc without actually dequeuing them when tokens are unavailable.

This peek operation creates a discrepancy between the parent and child qdisc queue length counters. When TBF later receives a high-priority packet, SKBPRIOs queue length may show a different value than whats reflected in its internal priority queue tracking, triggering the assertion.

The fix removes this overly strict assertions in SKBPRIO, they are not necessary at all.

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/034b293bf17c124fec0f0e663f81203b00aa7a50
• https://git.kernel.org/stable/c/1284733bab736e598341f1d3f3b94e2a322864a8
• https://git.kernel.org/stable/c/1dcc144c322a8d526b791135604c0663f1af9d85
• https://git.kernel.org/stable/c/2286770b07cb5268c03d11274b8efd43dff0d380
• https://git.kernel.org/stable/c/2f35b7673a3aa3d09b3eb05811669622ebaa98ca
• https://git.kernel.org/stable/c/32ee79682315e6d3c99947b3f38b078a09a66919
• https://git.kernel.org/stable/c/7abc8318ce0712182bf0783dcfdd9a6a8331160e
• https://git.kernel.org/stable/c/864ca690ff135078d374bd565b9872f161c614bc
• https://git.kernel.org/stable/c/ce8fe975fd99b49c29c42e50f2441ba53112b2e8
• https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
• https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html