---
id: "CVE-2026-99159"
kind: "vulnerability"
aliases: ["CVE-2026-99159"]
title: "Linux kernel: persistent ring buffer index error can crash trace mapping"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "runtime", "tracing"]
not_affected_if: ["default-config"]
published_at: "2026-10-28T11:17:36+00:00"
first_seen_at: "2026-10-28T11:32:36+00:00"
updated_at: "2026-10-28T11:35:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99159", "first_seen_at": "2026-10-28T11:32:36+00:00"}]
---

# Linux kernel: persistent ring buffer index error can crash trace mapping

On a persistent ring buffer, the kernel computes one sub-buffer index too high, leaving a NULL pointer that is dereferenced when userspace maps trace_pipe_raw. The sources describe a crash on that mapping and loss of the previous boot's trace data, and do not describe code execution.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Update to a Linux kernel release that includes the upstream commit 'ring-buffer: Fix the sub-buffer array base in rb_meta_subbuf_idx()'
- unknown

## Timeline

- 2026-10-28T11:32:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99159

## From the sources

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

ring-buffer: Fix the sub-buffer array base in rb_meta_subbuf_idx()

On a persistent ring buffer, rb_meta_subbuf_idx() can return an index one
sub-buffer too high.  rb_setup_ids_meta_page() then fills subbuf_ids[]
shifted by one and leaves subbuf_ids[0] NULL, which __rb_map_vma()
dereferences when userspace maps trace_pipe_raw.  rb_update_meta_reader()
writes two such indices into meta->buffers[], which rb_cpu_meta_valid()
would reject on the next boot, discarding the previous boot's trace.

A CPU's sub-buffer array starts after its meta header and the nr_subbufs
integers that follow, aligned up to a sub-buffer.  rb_meta_subbuf_idx()
inverts that calculation but skips only the integers, not the header, so
its base is one sub-buffer low whenever the omitted header size crosses
the alignment boundary.

Invert the calculation with rb_subbufs_from_meta() rather than repeating
it.  rb_range_buffer() maps an index back to an address through the same
helper, so the two directions can no longer disagree.

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