syscall: allow \x00-prefixed unix abstract socket to use full path length

Fixes #70893

Change-Id: Ia0aaa497dad335fe962d52d3f115d26e8046e36f
GitHub-Last-Rev: 7dd663678d
GitHub-Pull-Request: golang/go#71851
Reviewed-on: https://go-review.googlesource.com/c/go/+/650875
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>

src/net/unixsock_linux_test.go

@@ -49,6 +49,23 @@ func TestUnixAutobindClose(t *testing.T) {
 	ln.Close()
 }
 
+func TestUnixAbstractLongNameNulStart(t *testing.T) {
+	// Create an abstract socket name that starts with a null byte ("\x00")
+	// whose length is the maximum of RawSockaddrUnix Path len
+	paddedAddr := make([]byte, len(syscall.RawSockaddrUnix{}.Path))
+	copy(paddedAddr, "\x00abstract_test")
+
+	la, err := ResolveUnixAddr("unix", string(paddedAddr))
+	if err != nil {
+		t.Fatal(err)
+	}
+	c, err := ListenUnix("unix", la)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.Close()
+}
+
 func TestUnixgramLinuxAbstractLongName(t *testing.T) {
 	if !testableNetwork("unixgram") {
 		t.Skip("abstract unix socket long name test")

src/net/unixsock_windows_test.go

@@ -10,6 +10,7 @@ import (
 	"internal/syscall/windows"
 	"os"
 	"reflect"
+	"syscall"
 	"testing"
 )
 
@@ -69,6 +70,27 @@ func TestUnixConnLocalWindows(t *testing.T) {
 	}
 }
 
+func TestUnixAbstractLongNameNulStart(t *testing.T) {
+	if !windows.SupportUnixSocket() {
+		t.Skip("unix test")
+	}
+
+	// Create an abstract socket name that starts with a null byte ("\x00")
+	// whose length is the maximum of RawSockaddrUnix Path len
+	paddedAddr := make([]byte, len(syscall.RawSockaddrUnix{}.Path))
+	copy(paddedAddr, "\x00abstract_test")
+
+	la, err := ResolveUnixAddr("unix", string(paddedAddr))
+	if err != nil {
+		t.Fatal(err)
+	}
+	c, err := ListenUnix("unix", la)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.Close()
+}
+
 func TestModeSocket(t *testing.T) {
 	if !windows.SupportUnixSocket() {
 		t.Skip("unix test")

src/syscall/syscall_linux.go

@@ -550,23 +550,29 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	if n > len(sa.raw.Path) {
 		return nil, 0, EINVAL
 	}
-	if n == len(sa.raw.Path) && name[0] != '@' {
+	// Abstract addresses start with NUL.
+	// '@' is also a valid way to specify abstract addresses.
+	isAbstract := n > 0 && (name[0] == '@' || name[0] == '\x00')
+
+	// Non-abstract named addresses are NUL terminated.
+	// The length can't use the full capacity as we need to add NUL.
+	if n == len(sa.raw.Path) && !isAbstract {
 		return nil, 0, EINVAL
 	}
 	sa.raw.Family = AF_UNIX
 	for i := 0; i < n; i++ {
 		sa.raw.Path[i] = int8(name[i])
 	}
-	// length is family (uint16), name, NUL.
-	sl := _Socklen(2)
-	if n > 0 {
-		sl += _Socklen(n) + 1
-	}
-	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
-		// Check sl > 3 so we don't change unnamed socket behavior.
+	// Length is family + name (+ NUL if non-abstract).
+	// Family is of type uint16 (2 bytes).
+	sl := _Socklen(2 + n)
+	if isAbstract {
+		// Abstract addresses are not NUL terminated.
+		// We rewrite '@' prefix to NUL here.
 		sa.raw.Path[0] = 0
-		// Don't count trailing NUL for abstract address.
-		sl--
+	} else if n > 0 {
+		// Add NUL for non-abstract named addresses.
+		sl++
 	}
 
 	return unsafe.Pointer(&sa.raw), sl, nil

src/syscall/syscall_windows.go

@@ -858,23 +858,29 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, int32, error) {
 	if n > len(sa.raw.Path) {
 		return nil, 0, EINVAL
 	}
-	if n == len(sa.raw.Path) && name[0] != '@' {
+	// Abstract addresses start with NUL.
+	// '@' is also a valid way to specify abstract addresses.
+	isAbstract := n > 0 && (name[0] == '@' || name[0] == '\x00')
+
+	// Non-abstract named addresses are NUL terminated.
+	// The length can't use the full capacity as we need to add NUL.
+	if n == len(sa.raw.Path) && !isAbstract {
 		return nil, 0, EINVAL
 	}
 	sa.raw.Family = AF_UNIX
 	for i := 0; i < n; i++ {
 		sa.raw.Path[i] = int8(name[i])
 	}
-	// length is family (uint16), name, NUL.
-	sl := int32(2)
-	if n > 0 {
-		sl += int32(n) + 1
-	}
-	if sa.raw.Path[0] == '@' || (sa.raw.Path[0] == 0 && sl > 3) {
-		// Check sl > 3 so we don't change unnamed socket behavior.
+	// Length is family + name (+ NUL if non-abstract).
+	// Family is of type uint16 (2 bytes).
+	sl := int32(2 + n)
+	if isAbstract {
+		// Abstract addresses are not NUL terminated.
+		// We rewrite '@' prefix to NUL here.
 		sa.raw.Path[0] = 0
-		// Don't count trailing NUL for abstract address.
-		sl--
+	} else if n > 0 {
+		// Add NUL for non-abstract named addresses.
+		sl++
 	}
 
 	return unsafe.Pointer(&sa.raw), sl, nil