---
id: CVE-2026-98503
title: 'packet: use ubuf_info completion for TX_RING packets'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  packet: use ubuf_info completion for TX_RING packets

  tpacket_snd sends skbs with frags pointing into its ring slots. Slots
  are released when skb->destructor is called.…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 <
    e67c455d79fbf709a94965f09a2be6bf4f4ba5fd
  - >-
    Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 <
    eda9bcb721f15a93746a99eabda33d80b86404fd
  - >-
    Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 <
    2a0c9afefc0ecea2cc30ccfbbbc98182a0986191
  - >-
    Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 <
    9518405613863d0bf0700927a21367f5942cf058
  - Linux 67f6fba765ef8cb19089d476e3c367212a2fbdfd
  - Linux f2a67e68dbaeae7c88e5522873d7b908911f9f77
  - Linux >= 4.14.86 < 4.15
  - Linux >= 4.19.7 < 4.20
  - Linux 4.20
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:17:03.904Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98503'
references:
  - url: 'https://git.kernel.org/stable/c/e67c455d79fbf709a94965f09a2be6bf4f4ba5fd'
  - url: 'https://git.kernel.org/stable/c/eda9bcb721f15a93746a99eabda33d80b86404fd'
  - url: 'https://git.kernel.org/stable/c/2a0c9afefc0ecea2cc30ccfbbbc98182a0986191'
  - url: 'https://git.kernel.org/stable/c/9518405613863d0bf0700927a21367f5942cf058'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.287Z'
---

## Overview

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

packet: use ubuf_info completion for TX_RING packets

tpacket_snd sends skbs with frags pointing into its ring slots. Slots
are released when skb->destructor is called.

A call to skb_orphan calls skb->destructor before the skb is freed.
This can cause the slot to be reused while still linked into the skb.

Switch to standard zerocopy completion (ubuf_info) so the slot is only
released once all references to the payload are freed or copied.
Restore skb->destructor to standard sock_wfree.

The ubuf_info completion callback can be called with a NULL skb, but
only from net_zcopy_put and related API, used by zerocopy implementations
that hold their own reference on the uarg, such as MSG_ZEROCOPY. This
uarg is only ever completed from skb_zcopy_clear, so skb is always set.

To prevent userspace from aliasing in-flight state on shared ring
slots, allocate tpacket_uarg per packet, rather than per slot. This
adds a small allocation to the transmit path. Use standard kmalloc to
allow backporting to stable kernels.

The uarg holds an sk_wmem_alloc reference, rather than an sk_refcnt
reference. packet_free_tx_ring waits on sk_wmem_alloc before freeing
the ring pages. Always allocate vec->deferred for tx_ring so page-backed
rings also wait on sk_wmem_alloc when skb_copy_ubufs drops page refs
before calling tpacket_ubuf_complete.

Drop the tx_ring.pg_vec test that tpacket_destruct_skb performed before
accessing the slot. The sk_wmem_alloc reference now guarantees that the
slot is valid. The test is also not sufficient by itself, as it reads
pg_vec without pg_vec_lock, so it can race with packet_set_ring.

As a result a slot is released when its payload is copied, which can
be before transmission (e.g., in skb_orphan_frags_rx). If copied
before skb_tx_timestamp() is called, no slot timestamp is recorded,
similar to when skb_orphan() was called early in the datapath before
this patch.

Revert the now unused previous skb_zcopy_.._nouarg infra.

Depends on commit 992cc9f94ca9 ("net/packet: defer vmalloc TX_RING
free until skbs finish").

## Affected

- `Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 < e67c455d79fbf709a94965f09a2be6bf4f4ba5fd`
- `Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 < eda9bcb721f15a93746a99eabda33d80b86404fd`
- `Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 < 2a0c9afefc0ecea2cc30ccfbbbc98182a0986191`
- `Linux >= 5cd8d46ea1562be80063f53c7c6a5f40224de623 < 9518405613863d0bf0700927a21367f5942cf058`
- `Linux 67f6fba765ef8cb19089d476e3c367212a2fbdfd`
- `Linux f2a67e68dbaeae7c88e5522873d7b908911f9f77`
- `Linux >= 4.14.86 < 4.15`
- `Linux >= 4.19.7 < 4.20`
- `Linux 4.20`

## Remediation

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