---
id: CVE-2026-99055
title: 'tcp: reject net_iov in zerocopy receive mapping hints'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tcp: reject net_iov in zerocopy receive mapping hints

  After copying a readable prefix, receive_fallback_to_copy() asks
  tcp_zerocopy_set_hint_for_skb() where page mappi…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 <
    563d3564513496b9ce3b3ba7a5154427554d0f06
  - >-
    Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 <
    1c7463ac0e99cc91c4eecc1b69a740ef1a619932
  - >-
    Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 <
    3aa6f536a95eb0617c313ae2eb76fdfa85331f85
  - >-
    Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 <
    8b1f0af1fd5fd113432233ed8a3862ee7c30a84f
  - Linux 6.12
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:22:39.451Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99055'
references:
  - url: 'https://git.kernel.org/stable/c/563d3564513496b9ce3b3ba7a5154427554d0f06'
  - url: 'https://git.kernel.org/stable/c/1c7463ac0e99cc91c4eecc1b69a740ef1a619932'
  - url: 'https://git.kernel.org/stable/c/3aa6f536a95eb0617c313ae2eb76fdfa85331f85'
  - url: 'https://git.kernel.org/stable/c/8b1f0af1fd5fd113432233ed8a3862ee7c30a84f'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.523Z'
---

## Overview

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

tcp: reject net_iov in zerocopy receive mapping hints

After copying a readable prefix, receive_fallback_to_copy() asks
tcp_zerocopy_set_hint_for_skb() where page mapping can resume. If the
next skb is unreadable, find_next_mappable_frag() passes its net_iov
fragment to can_map_frag().

skb_frag_page() returns NULL for a net_iov, but can_map_frag()
dereferences it in PageCompound(). A v7.2 KASAN run on a connected TCP
socket with 64 readable bytes followed by a 4096-byte NET_IOV_DMABUF
fragment reported:

  BUG: KASAN: null-ptr-deref in can_map_frag
  tcp_zerocopy_receive -> can_map_frag
  Kernel panic - not syncing: KASAN: panic_on_warn set

The diagnostic inserted the net_iov directly because the test host has
no devmem-capable NIC. Hardware end-to-end reachability remains untested
and requires CONFIG_NET_DEVMEM plus a supported DMA-buf-bound RX queue.

Reject all net_iov fragments before skb_frag_page(). This covers both
DMABUF and IOURING net_iov types while leaving page-backed checks
unchanged. With the guard, the same queue copied the readable prefix,
returned a 4096-byte skip hint, and completed without a fault.

## Affected

- `Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 563d3564513496b9ce3b3ba7a5154427554d0f06`
- `Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 1c7463ac0e99cc91c4eecc1b69a740ef1a619932`
- `Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 3aa6f536a95eb0617c313ae2eb76fdfa85331f85`
- `Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 8b1f0af1fd5fd113432233ed8a3862ee7c30a84f`
- `Linux 6.12`

## Remediation

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