CVE-2026-63830

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, sk_msg_shift_left/right(), sk_msg_xfer(), and tls_split_open_record(), including the partial tail entry created during TLS open-record splitting.

Weakness

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

Affected Software

Potential Mitigations

• Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
• Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
• For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
• One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.

References

• https://git.kernel.org/stable/c/0eb4c16c4adb262763bda870a8ed38a1a9dec7ec
• https://git.kernel.org/stable/c/1acdd14c0990dd1cd4b6534f00366d2e6dfce05f
• https://git.kernel.org/stable/c/21ed9540a8e1906dfcbc1bb82ba9b4de4fa4bd6d
• https://git.kernel.org/stable/c/31a110642b5fb5e61940cbcfb503445ac4f28017
• https://git.kernel.org/stable/c/406e8a651a7b854c41fecd5117bb282b3a6c2c6b
• https://git.kernel.org/stable/c/9bb86d8184b37503816150c4a6ad3c17dfdbe827
• https://git.kernel.org/stable/c/d22cc92bc41290e5783a72375e0843d9435f6001
• https://git.kernel.org/stable/c/f126eed589eec6f201405abbc398844042ef6d57