---
id: CVE-2026-99033
title: 'net/packet: guard the ll header push in packet_rcv_spkt()'
summary: "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/packet: guard the ll header push in packet_rcv_spkt()\n\npacket_rcv_spkt() restores the link layer header with\n\n\tskb_push(skb, skb->data - skb_mac_header(skb));\n\nThat…"
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 <
    d8a24b9e1774a93943caf68d48c5e17be432220b
  - >-
    Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 <
    31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be
  - >-
    Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 <
    3efe0e0944157fdd2072b4dc7eb0491a317ed272
  - >-
    Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 <
    00fbf71e74115f7628fc0880b855434b1e70c40c
  - >-
    Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 <
    28bc1ef699610ee09ce3d46a00552f5a0a0144bd
  - Linux dadddde259a19105ee69e788835f4d4552767aa9
  - Linux >= 5.9.13 < 5.10
  - Linux 5.10
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:21:37.662Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99033'
references:
  - url: 'https://git.kernel.org/stable/c/d8a24b9e1774a93943caf68d48c5e17be432220b'
  - url: 'https://git.kernel.org/stable/c/31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be'
  - url: 'https://git.kernel.org/stable/c/3efe0e0944157fdd2072b4dc7eb0491a317ed272'
  - url: 'https://git.kernel.org/stable/c/00fbf71e74115f7628fc0880b855434b1e70c40c'
  - url: 'https://git.kernel.org/stable/c/28bc1ef699610ee09ce3d46a00552f5a0a0144bd'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.531Z'
---

## Overview

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

net/packet: guard the ll header push in packet_rcv_spkt()

packet_rcv_spkt() restores the link layer header with

	skb_push(skb, skb->data - skb_mac_header(skb));

That subtraction is only meaningful when the device actually has a link
layer header.  packet_rcv() and tpacket_rcv() both wrap it in
dev_has_header(), which is also the predicate the block comment at the
top of the file states the restore in terms of; packet_rcv_spkt() does
not.  commit d549699048b4 ("net/packet: fix packet receive on L3
devices without visible hard header") introduced the helper and changed
the two call sites, and this one stayed behind.

A device without a visible ll header can leave skb->mac_header at the
0xFFFF sentinel that __alloc_skb() initialises it to.  A CAN skb does:
init_can_skb() sets pkt_type and ip_summed but does not reset the
headers, and commit 9f10374bb024 ("can: remove private CAN skb
headroom infrastructure") dropped the skb_reset_*_header() calls that
used to be there.  skb_mac_header() is then 0xFFFF, the length becomes
a large negative number and skb_push() reports it through
skb_under_panic() -- from softirq context, so it is a full system panic
even with panic_on_oops=0:

  skbuff: skb_under_panic: text:ffffffff8bd21bc1 len:-65455 put:-65471 head:... data:... tail:0x50 end:0x180 dev:can0
  kernel BUG at net/core/skbuff.c:214!
  RIP: 0010:skb_panic+0x50/0x60
  Call Trace:
   <IRQ>
   skb_push+0x38/0x40
   packet_rcv_spkt+0xe1/0x170
   __netif_receive_skb_core.constprop.0+0x7e8/0xd30
   ...
  Kernel panic - not syncing: Fatal exception in interrupt

The socket type is reachable: packet_create() accepts SOCK_PACKET
alongside SOCK_RAW and SOCK_DGRAM behind the same CAP_NET_RAW check,
and neither the socket length nor a capability check keeps it away
from a CAN interface.

The missing skb_reset_*_header() calls in init_can_skb() are a
regression in their own right and are being fixed separately, but a
packet socket should not turn a link layer that did not initialise its
mac header into a kernel panic.  Guard the push the way the other two
receive paths do.

Tested on v7.3-rc5 under QEMU with a slcan device on a pty, which is
the driver RX path: vcan does not reproduce it, because can_send()
resets the headers on the way out.  One SOCK_PACKET socket bound to
can0 and one frame written into the line discipline panics an
unpatched kernel with the trace above; the same image with this patch
prints no panic and powers off normally.  Both kernels are this tree,
defconfig plus CONFIG_CAN_SLCAN=y, differing only in this hunk.

## Affected

- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < d8a24b9e1774a93943caf68d48c5e17be432220b`
- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be`
- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 3efe0e0944157fdd2072b4dc7eb0491a317ed272`
- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 00fbf71e74115f7628fc0880b855434b1e70c40c`
- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 28bc1ef699610ee09ce3d46a00552f5a0a0144bd`
- `Linux dadddde259a19105ee69e788835f4d4552767aa9`
- `Linux >= 5.9.13 < 5.10`
- `Linux 5.10`

## Remediation

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