---
id: CVE-2026-90359
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Reject >8 byte return values on return-reading trampoline paths

  btf_distill_func_proto() builds the function model used for the
  fentry/fexit/fmod_ret/fsession tra…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  bpf: Reject >8 byte return values on return-reading trampoline paths

  btf_distill_func_proto() builds the function model used for the
  fentry/fexit/fmod_ret/fsession tra…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= fec56f5890d93fc2ed74166c397dc186b1c25951 <
    d36ac53fc83baf843c51b7afd6d2471f36b713d8
  - >-
    Linux >= fec56f5890d93fc2ed74166c397dc186b1c25951 <
    c48796aa6c392cde93946e5d5a9a1f1b1cf72feb
  - Linux 5.5
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:17:34.810'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90359'
references:
  - url: 'https://git.kernel.org/stable/c/c48796aa6c392cde93946e5d5a9a1f1b1cf72feb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d36ac53fc83baf843c51b7afd6d2471f36b713d8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.812Z'
epss: 0.00189
epssPercentile: 0.08852
---

## Overview

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

bpf: Reject >8 byte return values on return-reading trampoline paths

btf_distill_func_proto() builds the function model used for the
fentry/fexit/fmod_ret/fsession trampolines and struct_ops. It has
accepted a 16-byte __int128 return value since the trampoline was
introduced: __get_type_size() returns the integer's type size, and the
return-type check only rejected ret < 0.

But the BPF trampoline preserves only 8 bytes of the return value (RAX on
x86, i.e. R0). For an attach type that reads the target's return value the
second half (RDX / R3) is neither saved nor restored, so a program
attached to a function returning a 16-byte value corrupts the value seen
by the real caller and itself observes only half of it. struct_ops
trampolines have the same limitation.

This affects the attach types that read the target's return value: fexit,
fmod_ret and fsession (plus the _multi variants of fexit and fsession),
and struct_ops. fentry/fentry_multi run before the target returns and are
unaffected.

Reject a >8 byte return value for these attach types in
bpf_check_attach_target() and bpf_check_attach_btf_id_multi(), and for
struct_ops in bpf_struct_ops_desc_init().

## Remediation

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