CVE-2026-99064: cipso: adjust cached option offsets when removing CIPSO

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

cipso: adjust cached option offsets when removing CIPSO

cipsov4skbuffdelattr() removes the CIPSO bytes but does not adjust cached offsets for options that follow them.

For example, with a valid 10-byte CIPSO option followed by a seven-byte RR option, parsing records rr at offset 30. Removing CIPSO moves RR to offset 20, while the cached offset remains 30. Consumers such as ipforwardoptions() and ipoptionsecho() then access the wrong bytes; the latter may interpret packet data as the option length and copy it into fixed-size option storage.

Mirror cipsov4delopt() and subtract cipsolen from the srr, rr, ts and routeralert offsets when they follow CIPSO. cipsolen is the distance the first memmove() shifts those options. The later header move and network-header reset relocate the bytes and their offset base together.