---
id: CVE-2026-98061
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Reject tail calls directly from callback frames

  A tail call from a non-zero frame is modeled as a return from that frame.
  The verifier makes R0 unknown and calls …
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Reject tail calls directly from callback frames

  A tail call from a non-zero frame is modeled as a return from that frame.
  The verifier makes R0 unknown and calls …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8 <
    617c8266e49f45747f71e74177646a63f72b7025
  - >-
    Linux >= e3245f8990431950d20631c72236d4e8cb2dcde8 <
    96d31b28263c429a56e4de85bcf744a5c320b3a3
  - >-
    Linux >= e3245f8990431950d20631c72236d4e8cb2dcde8 <
    266aa4ad0b2e82397cd9045752c9bff03d98eddd
  - Linux >= 6.18.2 < 6.18.53
  - Linux 6.19
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:35.110'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98061'
references:
  - url: 'https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.843Z'
---

## Overview

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

bpf: Reject tail calls directly from callback frames

A tail call from a non-zero frame is modeled as a return from that frame.
The verifier makes R0 unknown and calls prepare_func_exit() for the taken
branch.

When the current frame is a synchronous callback, prepare_func_exit()
enforces the callback return-value contract and marks R0 precise. Since the
tail-call path synthesized R0 rather than deriving it from an instruction,
precision backtracking reaches the callback-calling instruction with R0
still requested and triggers the "callback unexpected regs" verifier bug.
A CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.

Tail calls reachable from callbacks are already rejected later by
check_max_stack_depth(). Reject a tail call made directly by a callback
before constructing the inconsistent return state, using the existing
diagnostic. Tail calls from ordinary subprograms keep their current
behavior.

## Remediation

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