unix: stop counting trailing NUL for abstract addresses starting with NUL

Changes trailing-NUL-counting behavior for abstract addresses
starting with the NUL character to be the same as abstract
addresses starting with the @ character.

For golang/go#63579.

Change-Id: I2f26de4bcf614c4635ad188b1afa3d14ebd9a95f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/535955
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Benny Siegert <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: F Y

unix/syscall_aix.go

@@ -106,7 +106,8 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	if n > 0 {
 		sl += _Socklen(n) + 1
 	}
-	if sa.raw.Path[0] == '@' {
+	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
+		// Check sl > 3 so we don't change unnamed socket behavior.
 		sa.raw.Path[0] = 0
 		// Don't count trailing NUL for abstract address.
 		sl--

unix/syscall_internal_linux_test.go

@@ -517,7 +517,7 @@ func TestSockaddrUnix_sockaddr(t *testing.T) {
 			slen: 2, // family (uint16)
 		},
 		{
-			name: "abstract",
+			name: "abstract_starting_with_at",
 			sa: &SockaddrUnix{
 				Name: "@",
 			},
@@ -526,6 +526,16 @@ func TestSockaddrUnix_sockaddr(t *testing.T) {
 			},
 			slen: 3, // family (uint16) + NULL
 		},
+		{
+			name: "abstract_starting_with_null",
+			sa: &SockaddrUnix{
+				Name: "\x00",
+			},
+			raw: &RawSockaddrUnix{
+				Family: AF_UNIX,
+			},
+			slen: 3, // family (uint16) + NULL
+		},
 		{
 			name: "named",
 			sa: &SockaddrUnix{

unix/syscall_linux.go

@@ -417,7 +417,8 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	if n > 0 {
 		sl += _Socklen(n) + 1
 	}
-	if sa.raw.Path[0] == '@' {
+	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
+		// Check sl > 3 so we don't change unnamed socket behavior.
 		sa.raw.Path[0] = 0
 		// Don't count trailing NUL for abstract address.
 		sl--

unix/syscall_solaris.go

@@ -128,7 +128,8 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	if n > 0 {
 		sl += _Socklen(n) + 1
 	}
-	if sa.raw.Path[0] == '@' {
+	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
+		// Check sl > 3 so we don't change unnamed socket behavior.
 		sa.raw.Path[0] = 0
 		// Don't count trailing NUL for abstract address.
 		sl--

windows/syscall_windows.go

@@ -970,7 +970,8 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, int32, error) {
 	if n > 0 {
 		sl += int32(n) + 1
 	}
-	if sa.raw.Path[0] == '@' {
+	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
+		// Check sl > 3 so we don't change unnamed socket behavior.
 		sa.raw.Path[0] = 0
 		// Don't count trailing NUL for abstract address.
 		sl--