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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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 label; payload_len after the call:

  case                         before fix   after fix   real length
  1000, unlabeled                    1016        1016          1016
  70000 GSO, payload_len 0             16           0         70016
  65530 GSO, grows past MAXPLEN        10           0         65546
  65540 GSO with a 24 byte hop
  header, shrinks below MAXPLEN     65528       65532         65532
  1000 with a 24 byte hop header      992         992           992

(0 means ipv6_payload_len() returns the real length.)  On the forward
path, with a client injecting unlabeled UDP through a router to a
server, the router adds the CALIPSO option and the server delivers all
datagrams (Udp6InDatagrams 5, Ip6InTruncatedPkts 0) with this patch.

The Linux kernel CVE team has assigned CVE-2026-99191 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.19 with commit 81fbc812132cbc72a0f933b19bfd3a829bd946e4 and fixed in 6.18.59 with commit 1c9fcfca51e3c5cd46dd72a4da74d56eff183513
	Issue introduced in 5.19 with commit 81fbc812132cbc72a0f933b19bfd3a829bd946e4 and fixed in 7.2.13 with commit 8ee0e03663826a76507048d58466b29321a57656
	Issue introduced in 5.19 with commit 81fbc812132cbc72a0f933b19bfd3a829bd946e4 and fixed in 7.3 with commit 8070ed578b6b9134e045627fb745c887a806d46e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-99191
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/ipv6/calipso.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1c9fcfca51e3c5cd46dd72a4da74d56eff183513
	https://git.kernel.org/stable/c/8ee0e03663826a76507048d58466b29321a57656
	https://git.kernel.org/stable/c/8070ed578b6b9134e045627fb745c887a806d46e