CVE-2026-99191 — calipso: keep BIG TCP payload_len in calipso_skbuff_setattr()

Affected: Linux

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

calipso: keep BIG TCP payload_len in calipso_skbuff_setattr()

calipso_skbuff_setattr() adjusts payload_len by the length of the option it inserts or resizes:

payload = ntohs(ip6_hdr->payload_len); ip6_hdr->payload_len = htons(payload + len_delta);

GRO can build BIG TCP packets larger than IPV6_MAXPLEN, and stores payload_len == 0 for them; ipv6_payload_len() then falls back to skb->len. For such a packet forwarded to a destination mapped to CALIPSO, the code above writes len_delta (or 65536 + len_delta when shrinking) into payload_len, and ipv6_payload_len() no longer falls back to skb->len. nf_tables, conntrack and sch_cake rely on it.

The same arithmetic also wraps when a packet grows past IPV6_MAXPLEN, and a BIG TCP packet that shrinks below IPV6_MAXPLEN should get its real length back.

Set payload_len from the skb length with ipv6_set_payload_len(), which stores 0 above IPV6_MAXPLEN and the real length otherwise, as ipv6_gro_complete() does. The network header was just reset to skb->data, so skb->len - sizeof(*ip6_hdr) is the payload length.

Tested on one kernel (arm64, QEMU) with SELinux permissive, a minimal mdp-generated policy (network_peer_controls=1), "netlabelctl calipso add pass doi:16" and a NetLabel mapping of fd00:2::/64 to CALIPSO DOI 16. calipso_skbuff_setattr() was called through netlbl_skbuff_setattr() from a test-only debugfs hook (not part of this patch) adding a level-only…

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CVE-2026-99191 — calipso: keep BIG TCP payload_len in calipso_skbuff_setattr()