# CVE-2026-90081: net/rds: use wq_has_sleeper() in rds_cong_map_updated()

> A race condition in the Linux kernel RDS module can cause senders to block indefinitely, leading to a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102839, BELL-CVE-2026-90081, DEBIAN-CVE-2026-90081, GHSA-23r9-76mg-5gpp, UBUNTU-CVE-2026-90081

## What is CVE-2026-90081?

CVE-2026-90081 is a vulnerability in Linux, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

net/rds: use wq_has_sleeper() in rds_cong_map_updated()

rds_cong_map_updated() runs after a peer's congestion map has been
rewritten (by rds_tcp_cong_recv() and rds_ib_cong_recv(), or the
clear-all in the loopback and IB send-completion paths).  It bumps
rds_cong_generation and then checks waitqueue_active() on
map->m_waitq and on rds_poll_waitq to decide whether anyone needs
waking.  atomic_inc() carries no ordering and waitqueue_active() is a
plain load, so nothing orders the map and generation stores before
the wait queue reads.  The waiters do the mirror image: rds_cong_wait()
adds itself to m_waitq and then tests the port bit, and rds_poll()
registers on rds_poll_waitq and then reads the generation.  That is
the store-buffering pattern described above waitqueue_active() in
include/linux/wait.h - the updater can observe an empty wait queue
while the waiter still observes the port as congested, and no wake-up
is issued.

rds_cong_wait() is an interruptible sleep with no timeout, so a
sender blocked on a congested port stays blocked until the next
congestion update from that peer arrives or a signal is delivered.
A poll() waiter misses the map-updated notification the same way.

Use wq_has_sleeper(), which is waitqueue_active() preceded by the
required full barrier, as rds_tcp_state_change() already does for
the same pattern.

## Which versions are affected by CVE-2026-90081?


## How do I fix CVE-2026-90081?

Apply the vendor's patch.

## Is CVE-2026-90081 being exploited?

There is no known exploitation of CVE-2026-90081 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90081 and fix it if it is affected.

What it is: CVE-2026-90081 is a vulnerability in Linux, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-90081 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-90081/ (Markdown: https://insights.sbomify.com/CVE-2026-90081/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90081
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90081
- OSV: https://osv.dev/vulnerability/CVE-2026-90081

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90081/
Summaries are generated and may contain mistakes; the official description above is the record.