# CVE-2026-72491: net/9p: fix race condition on rdma->state in trans_rdma.c

> A race condition in the Linux kernel's 9P RDMA transport allows state corruption, potentially leading to use-after-free and code execution or denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72491, DEBIAN-CVE-2026-72491, GHSA-gf38-f295-35cc, UBUNTU-CVE-2026-72491

## What is CVE-2026-72491?

CVE-2026-72491 is a critical vulnerability in Linux, published on 15 Aug 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/9p: fix race condition on rdma->state in trans_rdma.c

The rdma->state field is modified without holding req_lock in both
recv_done() and p9_cm_event_handler(), while rdma_request() accesses
the same field under the req_lock spinlock. This inconsistent locking
creates a race condition:

- recv_done() running in softirq completion context sets
  rdma->state = P9_RDMA_FLUSHING without acquiring req_lock

- p9_cm_event_handler() modifies rdma->state at multiple points
  (ADDR_RESOLVED, ROUTE_RESOLVED, ESTABLISHED, CLOSED) without
  req_lock

- rdma_request() uses spin_lock_irqsave(&rdma->req_lock, flags) to
  protect the read-modify-write of rdma->state

The race can cause lost state transitions: recv_done() or the CM
event handler could set state to FLUSHING/CLOSED while rdma_request()
is concurrently checking or modifying state under the lock, leading to
the FLUSHING transition being silently overwritten by CLOSING. This
corrupts the connection state machine and can cause use-after-free on
RDMA request objects during teardown.

Fix by adding req_lock protection to all rdma->state modifications in
recv_done() and p9_cm_event_handler(), matching the pattern already
used in rdma_request(). Use spin_lock_irqsave/spin_unlock_irqrestore
in the CM event handler since it can race with recv_done() which runs
in softirq context.

Tested with a kernel module that races two threads (simulating
rdma_request and recv_done/CM handler) on rdma->state with proper
locking: 5.5M+ FLUSHING writes over 27M iterations with 0 lost
transitions.

## Which versions are affected by CVE-2026-72491?


## How do I fix CVE-2026-72491?

Apply the vendor's patch.

## Is CVE-2026-72491 being exploited?

There is no known exploitation of CVE-2026-72491 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72491 and fix it if it is affected.

What it is: CVE-2026-72491 is a critical vulnerability in Linux, published on 15 Aug 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-2026-72491 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-2026-72491/ (Markdown: https://insights.sbomify.com/CVE-2026-72491/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72491
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72491
- OSV: https://osv.dev/vulnerability/CVE-2026-72491

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72491/
Summaries are generated and may contain mistakes; the official description above is the record.