---
id: CVE-2025-39813
title: 'ftrace: Fix potential warning in trace_printk_seq during ftrace_dump'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ftrace: Fix potential warning in trace_printk_seq during ftrace_dump

  When calling ftrace_dump_one() concurrently with reading trace_pipe,
  a WARN_ON_ONCE() in trace_pri…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    f299353e7ccbcc5c2ed8993c48fbe7609cbe729a
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    5ab0ec206deb99eb3baf8f1d7602aeaa91dbcc85
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    a6f0f8873cc30fd4543b09adf03f7f51d293f0e6
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    e80ff23ba8bdb0f41a1afe2657078e4097d13a9a
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    28c8fb7ae2ad27d81c8de3c4fe608c509f6a18aa
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    ced94e137e6cd5e79c65564841d3b7695d0f5fa3
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    fbd4cf7ee4db65ef36796769fe978e9eba6f0de4
  - >-
    Linux >= d769041f865330034131525ee6a7f72eb4af2a24 <
    4013aef2ced9b756a410f50d12df9ebe6a883e4a
  - Linux 2.6.28
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T21:12:05.539187Z'
published: '2025-09-16'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T21:12:59.108Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39813'
references:
  - url: 'https://git.kernel.org/stable/c/f299353e7ccbcc5c2ed8993c48fbe7609cbe729a'
  - url: 'https://git.kernel.org/stable/c/5ab0ec206deb99eb3baf8f1d7602aeaa91dbcc85'
  - url: 'https://git.kernel.org/stable/c/a6f0f8873cc30fd4543b09adf03f7f51d293f0e6'
  - url: 'https://git.kernel.org/stable/c/e80ff23ba8bdb0f41a1afe2657078e4097d13a9a'
  - url: 'https://git.kernel.org/stable/c/28c8fb7ae2ad27d81c8de3c4fe608c509f6a18aa'
  - url: 'https://git.kernel.org/stable/c/ced94e137e6cd5e79c65564841d3b7695d0f5fa3'
  - url: 'https://git.kernel.org/stable/c/fbd4cf7ee4db65ef36796769fe978e9eba6f0de4'
  - url: 'https://git.kernel.org/stable/c/4013aef2ced9b756a410f50d12df9ebe6a883e4a'
tags:
  - cve.org
epss: 0.00121
epssPercentile: 0.01928
ingestedAt: '2026-11-05T22:38:32.030Z'
---

## Overview

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

ftrace: Fix potential warning in trace_printk_seq during ftrace_dump

When calling ftrace_dump_one() concurrently with reading trace_pipe,
a WARN_ON_ONCE() in trace_printk_seq() can be triggered due to a race
condition.

The issue occurs because:

CPU0 (ftrace_dump)                              CPU1 (reader)
echo z > /proc/sysrq-trigger

!trace_empty(&iter)
trace_iterator_reset(&iter) <- len = size = 0
                                                cat /sys/kernel/tracing/trace_pipe
trace_find_next_entry_inc(&iter)
  __find_next_entry
    ring_buffer_empty_cpu <- all empty
  return NULL

trace_printk_seq(&iter.seq)
  WARN_ON_ONCE(s->seq.len >= s->seq.size)

In the context between trace_empty() and trace_find_next_entry_inc()
during ftrace_dump, the ring buffer data was consumed by other readers.
This caused trace_find_next_entry_inc to return NULL, failing to populate
`iter.seq`. At this point, due to the prior trace_iterator_reset, both
`iter.seq.len` and `iter.seq.size` were set to 0. Since they are equal,
the WARN_ON_ONCE condition is triggered.

Move the trace_printk_seq() into the if block that checks to make sure the
return value of trace_find_next_entry_inc() is non-NULL in
ftrace_dump_one(), ensuring the 'iter.seq' is properly populated before
subsequent operations.

## Affected

- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < f299353e7ccbcc5c2ed8993c48fbe7609cbe729a`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < 5ab0ec206deb99eb3baf8f1d7602aeaa91dbcc85`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < a6f0f8873cc30fd4543b09adf03f7f51d293f0e6`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < e80ff23ba8bdb0f41a1afe2657078e4097d13a9a`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < 28c8fb7ae2ad27d81c8de3c4fe608c509f6a18aa`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < ced94e137e6cd5e79c65564841d3b7695d0f5fa3`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < fbd4cf7ee4db65ef36796769fe978e9eba6f0de4`
- `Linux >= d769041f865330034131525ee6a7f72eb4af2a24 < 4013aef2ced9b756a410f50d12df9ebe6a883e4a`
- `Linux 2.6.28`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.