CVE-2026-74287: sctp: validate embedded address parameter length

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

sctp: validate embedded address parameter length

sctpverifyasconf() and sctpverifyparam() only validate ADDIP, DELIP, and SETPRIMARY parameters against a fixed minimum size of sizeof(struct sctpaddipparam) + sizeof(struct sctpparamhdr). This ensures the outer parameter is large enough to contain an embedded address parameter header, but does not verify that the embedded address parameter's declared length fits within the bounds of the outer parameter.

Later, sctpprocessparam() and sctpprocessasconfparam() extract the embedded address parameter and pass it to af->fromaddrparam(), which uses the address parameter length to parse the variable-length address payload. A malformed peer can therefore advertise an embedded address parameter length that exceeds the remaining bytes in the enclosing parameter.

Validate that addrparam->p.length does not exceed the space available after the sctpaddipparam header before processing the embedded address parameter. Reject malformed parameters when the embedded address length extends beyond the enclosing parameter bounds.

This prevents out-of-bounds reads when parsing malformed parameters carried in INIT or ASCONF processing paths.