fix: set write permissions for group and other (#1405)

Fixes #1403.

internal/proxy/proxy.go

@@ -626,6 +626,12 @@ func newSocketMount(ctx context.Context, conf *Config, pc *portConfig, inst Inst
 	if err != nil {
 		return nil, err
 	}
+	// Change file permisions to allow access for user, group, and other.
+	if network == "unix" {
+		// Best effort. If this call fails, group and other won't have write
+		// access.
+		_ = os.Chmod(address, 0777)
+	}
 	opts := conf.DialOptions(inst)
 	m := &socketMount{inst: inst.Name, dialOpts: opts, listener: ln}
 	return m, nil

internal/proxy/proxy_other_test.go

@@ -17,6 +17,11 @@
 
 package proxy_test
 
+import (
+	"os"
+	"testing"
+)
+
 var (
 	pg         = "proj:region:pg"
 	pg2        = "proj:region:pg2"
@@ -25,3 +30,13 @@ var (
 	sqlserver  = "proj:region:sqlserver"
 	sqlserver2 = "proj:region:sqlserver2"
 )
+
+func verifySocketPermissions(t *testing.T, addr string) {
+	fi, err := os.Stat(addr)
+	if err != nil {
+		t.Fatalf("os.Stat(%v): %v", addr, err)
+	}
+	if fm := fi.Mode(); fm != 0777|os.ModeSocket {
+		t.Fatalf("file mode: want = %v, got = %v", 0777|os.ModeSocket, fm)
+	}
+}

internal/proxy/proxy_test.go

@@ -283,6 +283,8 @@ func TestClientInitialization(t *testing.T) {
 			}
 
 			for _, addr := range tc.wantUnixAddrs {
+				verifySocketPermissions(t, addr)
+
 				conn, err := net.Dial("unix", addr)
 				if err != nil {
 					t.Fatalf("want error = nil, got = %v", err)

internal/proxy/proxy_windows_test.go

@@ -14,7 +14,10 @@
 
 package proxy_test
 
-import "strings"
+import (
+	"strings"
+	"testing"
+)
 
 var (
 	pg         = strings.ReplaceAll("proj:region:pg", ":", ".")
@@ -24,3 +27,9 @@ var (
 	sqlserver  = strings.ReplaceAll("proj:region:sqlserver", ":", ".")
 	sqlserver2 = strings.ReplaceAll("proj:region:sqlserver2", ":", ".")
 )
+
+func verifySocketPermissions(t *testing.T, addr string) {
+	// On Linux and Darwin, we check that the socket named by addr exists with
+	// os.Stat. That operation is not supported on Windows.
+	// See https://github.com/microsoft/Windows-Containers/issues/97#issuecomment-887713195
+}