---
id: CVE-2026-23316
title: 'net: ipv4: fix ARM64 alignment fault in multipath hash seed'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: ipv4: fix ARM64 alignment fault in multipath hash seed

  `struct sysctl_fib_multipath_hash_seed` contains two u32 fields
  (user_seed and mp_seed), making it an 8-byt…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 <
    4bdc94d45d5459f0149085dfc1efe733c8e14f11
  - >-
    Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 <
    7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199
  - >-
    Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 <
    607e923a3c1b2120de430b3dcde25ed8ad213c0a
  - >-
    Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 <
    4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f
  - Linux 6.11
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T21:26:49.330326Z'
published: '2026-03-25'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T21:33:38.599Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23316'
references:
  - url: 'https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11'
  - url: 'https://git.kernel.org/stable/c/7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199'
  - url: 'https://git.kernel.org/stable/c/607e923a3c1b2120de430b3dcde25ed8ad213c0a'
  - url: 'https://git.kernel.org/stable/c/4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f'
tags:
  - cve.org
epss: 0.00127
epssPercentile: 0.02368
ingestedAt: '2026-11-05T22:38:32.117Z'
---

## Overview

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

net: ipv4: fix ARM64 alignment fault in multipath hash seed

`struct sysctl_fib_multipath_hash_seed` contains two u32 fields
(user_seed and mp_seed), making it an 8-byte structure with a 4-byte
alignment requirement.

In `fib_multipath_hash_from_keys()`, the code evaluates the entire
struct atomically via `READ_ONCE()`:

    mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed;

While this silently works on GCC by falling back to unaligned regular
loads which the ARM64 kernel tolerates, it causes a fatal kernel panic
when compiled with Clang and LTO enabled.

Commit e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire
when CONFIG_LTO=y") strengthens `READ_ONCE()` to use Load-Acquire
instructions (`ldar` / `ldapr`) to prevent compiler reordering bugs
under Clang LTO. Since the macro evaluates the full 8-byte struct,
Clang emits a 64-bit `ldar` instruction. ARM64 architecture strictly
requires `ldar` to be naturally aligned, thus executing it on a 4-byte
aligned address triggers a strict Alignment Fault (FSC = 0x21).

Fix the read side by moving the `READ_ONCE()` directly to the `u32`
member, which emits a safe 32-bit `ldar Wn`.

Furthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire
struct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis
shows that Clang splits this 8-byte write into two separate 32-bit
`str` instructions. While this avoids an alignment fault, it destroys
atomicity and exposes a tear-write vulnerability. Fix this by
explicitly splitting the write into two 32-bit `WRITE_ONCE()`
operations.

Finally, add the missing `READ_ONCE()` when reading `user_seed` in
`proc_fib_multipath_hash_seed()` to ensure proper pairing and
concurrency safety.

## Affected

- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4bdc94d45d5459f0149085dfc1efe733c8e14f11`
- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199`
- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 607e923a3c1b2120de430b3dcde25ed8ad213c0a`
- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f`
- `Linux 6.11`

## Remediation

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