unix: add SetsockoptTCPMD5Sig on linux

This allows to set the TCP MD5 signature (see
https://www.rfc-editor.org/rfc/rfc2385) using TCPMD5Sig introduced in CL
106656.

Also export the storage data field in SockaddrStorage and convert it to
a byte array so the address in TCPMD5Sig.Addr can be set from an net.IP
without conversion.

Change-Id: I6bccfab57c188fcef857a6a3c514c943ca00b670
Reviewed-on: https://go-review.googlesource.com/c/sys/+/472835
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>

unix/mkpost.go

@@ -110,6 +110,15 @@ func main() {
 	icmpV6Regex := regexp.MustCompile(`type (ICMPv6Filter) struct {(\s+)X__icmp6_filt(\s+\S+\s+)}`)
 	b = icmpV6Regex.ReplaceAll(b, []byte("type $1 struct {${2}Filt$3}"))
 
+	// Intentionally export address storage field in SockaddrStorage convert it to [N]byte.
+	convertSockaddrStorageData := regexp.MustCompile(`(X__ss_padding)\s+\[(\d+)\]u?int8`)
+	sockaddrStorageType := regexp.MustCompile(`type SockaddrStorage struct {[^}]*}`)
+	sockaddrStorageStructs := sockaddrStorageType.FindAll(b, -1)
+	for _, s := range sockaddrStorageStructs {
+		newNames := convertSockaddrStorageData.ReplaceAll(s, []byte("Data [$2]byte"))
+		b = bytes.Replace(b, s, newNames, 1)
+	}
+
 	// If we have empty Ptrace structs, we should delete them. Only s390x emits
 	// nonempty Ptrace structs.
 	ptraceRexexp := regexp.MustCompile(`type Ptrace((Psw|Fpregs|Per) struct {\s*})`)

unix/syscall_linux.go

@@ -1364,6 +1364,10 @@ func SetsockoptTCPRepairOpt(fd, level, opt int, o []TCPRepairOpt) (err error) {
 	return setsockopt(fd, level, opt, unsafe.Pointer(&o[0]), uintptr(SizeofTCPRepairOpt*len(o)))
 }
 
+func SetsockoptTCPMD5Sig(fd, level, opt int, s *TCPMD5Sig) error {
+	return setsockopt(fd, level, opt, unsafe.Pointer(s), unsafe.Sizeof(*s))
+}
+
 // Keyctl Commands (http://man7.org/linux/man-pages/man2/keyctl.2.html)
 
 // KeyctlInt calls keyctl commands in which each argument is an int.