---
id: CVE-2026-98570
title: 'net: ipv6: keep room for the mac header in dst_dev_overhead()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: ipv6: keep room for the mac header in dst_dev_overhead()

  The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as
  the length they are about to push …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= dce525185bc92864e5a318040285ee070563fe34 <
    36c07127924f11fc5741a780abcaaf808fe9ef13
  - >-
    Linux >= dce525185bc92864e5a318040285ee070563fe34 <
    87cd6b717e4069dca34e0866e57eaeb44d3b173e
  - Linux 8471e228448a818e4c27cab4b681b2e758e46cf5
  - Linux c432cd18a07b623651ed15ea167bd303467004cc
  - Linux 634710a372ba65bee667c2f6e58a97658c639eab
  - Linux c447c5a9c47bb4858ab12bf90879fe595d2b7f46
  - Linux ab9de9c48316d2622d3bf353916b99971570e2c9
  - Linux 2fcc9f3798ef82399564d247458e69abd10e683b
  - Linux 371d8dc298b4f59e99b4564ac5d906fce0932c69
  - Linux b26f015dfb07b6be12d005a0ed0c5c43b7bedbf3
  - Linux c0b11dc50590e10590b39dcda79835cd32f49d00
  - Linux 4c12c3c8abd8b888945d31e7bdbb0d8b73032fc5
  - Linux 25d8e065c7972dc98fd7a4cac322d5367eaede88
  - Linux 4a855c5aec41bf84922224ab7a74e088776e3ac4
  - Linux a9f0407414e16176fdbbbd298c9e18d6dfdf96bc
  - Linux >= 6.12.16 < 6.13
  - Linux >= 6.13.4 < 6.14
  - Linux >= 5.15.179 < 5.16
  - Linux >= 6.1.130 < 6.2
  - Linux >= 6.6.81 < 6.7
  - Linux >= 5.10.235 < 5.11
  - Linux 6.14
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:18:36.308Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98570'
references:
  - url: 'https://git.kernel.org/stable/c/36c07127924f11fc5741a780abcaaf808fe9ef13'
  - url: 'https://git.kernel.org/stable/c/87cd6b717e4069dca34e0866e57eaeb44d3b173e'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.258Z'
---

## Overview

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

net: ipv6: keep room for the mac header in dst_dev_overhead()

The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as
the length they are about to push plus dst_dev_overhead(), then push the
new headers and rebuild the mac header below them with
skb_mac_header_rebuild().  That rebuild needs skb->mac_len of headroom,
but dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device,
16 bytes for plain Ethernet.

Where the mac header is longer than that, as it is on ingress through a
VLAN device with reorder_hdr off, the rebuild runs out of room:
skb_set_mac_header(skb, -skb->mac_len) computes a negative offset,
stores it unchecked in the u16 skb->mac_header, and the memmove that
follows writes skb->mac_len bytes about 64 KB past skb->head.
Forwarding plain ping6 traffic through such a device reproduces it on
all five seg6 encapsulation modes and on the rpl and ioam6 inline paths;
skb->mac_header comes back as 65534 on a 704-byte head.

Return the larger of the two.  The helper already returns skb->mac_len
when it has no dst, so this only makes the other branch agree, and it
covers every caller rather than each call site in turn.

## Affected

- `Linux >= dce525185bc92864e5a318040285ee070563fe34 < 36c07127924f11fc5741a780abcaaf808fe9ef13`
- `Linux >= dce525185bc92864e5a318040285ee070563fe34 < 87cd6b717e4069dca34e0866e57eaeb44d3b173e`
- `Linux 8471e228448a818e4c27cab4b681b2e758e46cf5`
- `Linux c432cd18a07b623651ed15ea167bd303467004cc`
- `Linux 634710a372ba65bee667c2f6e58a97658c639eab`
- `Linux c447c5a9c47bb4858ab12bf90879fe595d2b7f46`
- `Linux ab9de9c48316d2622d3bf353916b99971570e2c9`
- `Linux 2fcc9f3798ef82399564d247458e69abd10e683b`
- `Linux 371d8dc298b4f59e99b4564ac5d906fce0932c69`
- `Linux b26f015dfb07b6be12d005a0ed0c5c43b7bedbf3`
- `Linux c0b11dc50590e10590b39dcda79835cd32f49d00`
- `Linux 4c12c3c8abd8b888945d31e7bdbb0d8b73032fc5`
- `Linux 25d8e065c7972dc98fd7a4cac322d5367eaede88`
- `Linux 4a855c5aec41bf84922224ab7a74e088776e3ac4`
- `Linux a9f0407414e16176fdbbbd298c9e18d6dfdf96bc`
- `Linux >= 6.12.16 < 6.13`
- `Linux >= 6.13.4 < 6.14`
- `Linux >= 5.15.179 < 5.16`
- `Linux >= 6.1.130 < 6.2`
- `Linux >= 6.6.81 < 6.7`
- `Linux >= 5.10.235 < 5.11`
- `Linux 6.14`

## Remediation

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