net: skmsg: preserve sg.copy across SG transforms

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.

Source published

19 Jul 2026 12:02:23 UTC

Source modified

19 Oct 2026 20:07:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 9.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L