---
id: CVE-2026-97921
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tracing: Free histogram the field rejected for a bad modifier

  Writing a hist trigger whose value or variable carries a modifier that is
  not allowed there leaks the fie…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tracing: Free histogram the field rejected for a bad modifier

  Writing a hist trigger whose value or variable carries a modifier that is
  not allowed there leaks the fie…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e30fbc618e97b38dbb49f1d44dcd0778d3f23b8c <
    e787361bb6b0026ea3eb4d3fa7a304c7fcb99555
  - >-
    Linux >= e30fbc618e97b38dbb49f1d44dcd0778d3f23b8c <
    b22dc0add7d72b8bd9cae3188db0dd65da1c8652
  - >-
    Linux >= e30fbc618e97b38dbb49f1d44dcd0778d3f23b8c <
    891c21f6d5673b2a519b536243bfc6dd2d35beb6
  - >-
    Linux >= e30fbc618e97b38dbb49f1d44dcd0778d3f23b8c <
    230234d12ce42ab04132a32c3a848f07a5d27a71
  - Linux 7403630eb94c1d664fb873f967427ef2f6ee3699
  - Linux 8d505d06d7330f5d67d3e5e9e1c647fb0b10ddad
  - Linux >= 6.1.33 < 6.2
  - Linux >= 6.3.7 < 6.4
  - Linux 6.4
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:19.160'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-97921'
references:
  - url: 'https://git.kernel.org/stable/c/230234d12ce42ab04132a32c3a848f07a5d27a71'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/891c21f6d5673b2a519b536243bfc6dd2d35beb6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b22dc0add7d72b8bd9cae3188db0dd65da1c8652'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e787361bb6b0026ea3eb4d3fa7a304c7fcb99555'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.889Z'
---

## Overview

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

tracing: Free histogram the field rejected for a bad modifier

Writing a hist trigger whose value or variable carries a modifier that is
not allowed there leaks the fields that were built for it.

__create_val_field() takes the field from parse_expr() and stores it in
hist_data->fields[] only after the modifier checks have run:

	hist_field = parse_expr(hist_data, file, field_str, flags, var_name,
				&n_subexprs);
	...
	if (hist_field->flags & HIST_FIELD_FL_VAR) {
		if (hist_field->flags & (...))
			goto err;
	} else {
		if (hist_field->flags & (...))
			goto err;
	}

	hist_data->fields[val_idx] = hist_field;

Both checks jump past that store, and the err label returns without
freeing anything. The error unwinds to create_hist_data(), which calls
destroy_hist_data() -> destroy_hist_fields(), and that reaches a field
only by walking fields[]. A field that never got there is unreachable.

commit e0213434fe3e ("tracing: Do not let histogram values have some
modifiers") set ret to -EINVAL and fell through to the store, which left
the field owned by fields[] and freed along with the rest of hist_data.
Splitting the check into a value case and a variable case replaced that
fall-through with a goto that skips it.

With CONFIG_DEBUG_KMEMLEAK, 200 writes of

  # echo 'hist:keys=prev_pid:vals=next_pid.log2' > \
	 events/sched/sched_switch/trigger

each correctly rejected with -EINVAL, leave 332 unreferenced objects
(63744 bytes) reported at create_hist_field(); 200 install and remove
cycles of a valid trigger leave none. A '.log2' field is two
allocations, since create_hist_field() puts the plain field in
operands[0] of the log2 field, and both are reported.

Use destroy_hist_field() rather than __destroy_hist_field() so that
operands[0] is freed as well. It returns early for HIST_FIELD_FL_VAR_REF,
which is what an operand owned by hist_data->var_refs[] needs; the
rejected field itself is never a var ref, because a var ref never carries
a modifier flag.

## Remediation

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