CVE-2026-63830

Technical Description

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

net: skmsg: preserve sg.copy across SG transforms

The sk_msg sg.copy bitmap is part of the scatterlist entry ownership

state. A set bit tells sk_msg_compute_data_pointers() not to expose the

entry through writable BPF ctx->data. This protects entries backed by

pages that are not private to the sk_msg, such as splice-backed file

page-cache pages.

Several sk_msg transform paths move, copy, split, or compact

msg->sg.data[] entries without moving the matching sg.copy bit. This can

make an externally backed entry arrive at a new slot with a clear copy

bit. A later SK_MSG verdict can then expose sg_virt(sge) as writable

ctx->data and BPF stores can modify the original page cache.

Keep sg.copy synchronized with sg.data[] whenever entries are

transferred, shifted, split, or copied into a new sk_msg. Clear the bit

when an entry is replaced by a newly allocated private page or freed.

This covers the BPF pull/push/pop helpers

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References