cmd/go: add support for GIT_ALLOW_PROTOCOL

Allows users to override the default secure protocol list by setting the
GIT_ALLOW_PROTOCOL environment variable.

Addresses #17299 for vcs.go.

Change-Id: If575861d2b1b04b59029fed7e5d12b49690af50a
Reviewed-on: https://go-review.googlesource.com/30135
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/alldocs.go

@@ -1127,6 +1127,10 @@
 // 		Whether the linker should use external linking mode
 // 		when using -linkmode=auto with code that uses cgo.
 // 		Set to 0 to disable external linking mode, 1 to enable it.
+// 	GIT_ALLOW_PROTOCOL
+// 		Defined by Git. A colon-separated list of schemes that are allowed to be used
+// 		with git fetch/clone. If set, any scheme not explicitly mentioned will be
+// 		considered insecure by 'go get'.
 //
 //
 // Import path syntax
@@ -1226,6 +1230,11 @@
 // each is tried in turn when downloading.  For example, a Git
 // download tries https://, then git+ssh://.
 //
+// By default, downloads are restricted to known secure protocols
+// (e.g. https, ssh). To override this setting for Git downloads, the
+// GIT_ALLOW_PROTOCOL environment variable can be set (For more details see:
+// 'go help environment').
+//
 // If the import path is not a known code hosting site and also lacks a
 // version control qualifier, the go tool attempts to fetch the import
 // over https/http and looks for a <meta> tag in the document's HTML

src/cmd/go/help.go

@@ -197,6 +197,11 @@ When a version control system supports multiple protocols,
 each is tried in turn when downloading.  For example, a Git
 download tries https://, then git+ssh://.
 
+By default, downloads are restricted to known secure protocols
+(e.g. https, ssh). To override this setting for Git downloads, the
+GIT_ALLOW_PROTOCOL environment variable can be set (For more details see:
+'go help environment').
+
 If the import path is not a known code hosting site and also lacks a
 version control qualifier, the go tool attempts to fetch the import
 over https/http and looks for a <meta> tag in the document's HTML
@@ -488,6 +493,10 @@ Special-purpose environment variables:
 		Whether the linker should use external linking mode
 		when using -linkmode=auto with code that uses cgo.
 		Set to 0 to disable external linking mode, 1 to enable it.
+	GIT_ALLOW_PROTOCOL
+		Defined by Git. A colon-separated list of schemes that are allowed to be used
+		with git fetch/clone. If set, any scheme not explicitly mentioned will be
+		considered insecure by 'go get'.
 	`,
 }
 

src/cmd/go/vcs.go

@@ -41,7 +41,7 @@ type vcsCmd struct {
 	resolveRepo func(v *vcsCmd, rootDir, remoteRepo string) (realRepo string, err error)
 }
 
-var isSecureScheme = map[string]bool{
+var defaultSecureScheme = map[string]bool{
 	"https":   true,
 	"git+ssh": true,
 	"bzr+ssh": true,
@@ -55,7 +55,25 @@ func (v *vcsCmd) isSecure(repo string) bool {
 		// If repo is not a URL, it's not secure.
 		return false
 	}
-	return isSecureScheme[u.Scheme]
+	return v.isSecureScheme(u.Scheme)
+}
+
+func (v *vcsCmd) isSecureScheme(scheme string) bool {
+	switch v.cmd {
+	case "git":
+		// GIT_ALLOW_PROTOCOL is an environment variable defined by Git. It is a
+		// colon-separated list of schemes that are allowed to be used with git
+		// fetch/clone. Any scheme not mentioned will be considered insecure.
+		if allow := os.Getenv("GIT_ALLOW_PROTOCOL"); allow != "" {
+			for _, s := range strings.Split(allow, ":") {
+				if s == scheme {
+					return true
+				}
+			}
+			return false
+		}
+	}
+	return defaultSecureScheme[scheme]
 }
 
 // A tagCmd describes a command to list available tags
@@ -612,7 +630,7 @@ func repoRootFromVCSPaths(importPath, scheme string, security securityMode, vcsP
 				match["repo"] = scheme + "://" + match["repo"]
 			} else {
 				for _, scheme := range vcs.scheme {
-					if security == secure && !isSecureScheme[scheme] {
+					if security == secure && !vcs.isSecureScheme(scheme) {
 						continue
 					}
 					if vcs.ping(scheme, match["repo"]) == nil {

src/cmd/go/vcs_test.go

@@ -229,6 +229,45 @@ func TestIsSecure(t *testing.T) {
 	}
 }
 
+func TestIsSecureGitAllowProtocol(t *testing.T) {
+	tests := []struct {
+		vcs    *vcsCmd
+		url    string
+		secure bool
+	}{
+		// Same as TestIsSecure to verify same behavior.
+		{vcsGit, "http://example.com/foo.git", false},
+		{vcsGit, "https://example.com/foo.git", true},
+		{vcsBzr, "http://example.com/foo.bzr", false},
+		{vcsBzr, "https://example.com/foo.bzr", true},
+		{vcsSvn, "http://example.com/svn", false},
+		{vcsSvn, "https://example.com/svn", true},
+		{vcsHg, "http://example.com/foo.hg", false},
+		{vcsHg, "https://example.com/foo.hg", true},
+		{vcsGit, "user@server:path/to/repo.git", false},
+		{vcsGit, "user@server:", false},
+		{vcsGit, "server:repo.git", false},
+		{vcsGit, "server:path/to/repo.git", false},
+		{vcsGit, "example.com:path/to/repo.git", false},
+		{vcsGit, "path/that/contains/a:colon/repo.git", false},
+		{vcsHg, "ssh://user@example.com/path/to/repo.hg", true},
+		// New behavior.
+		{vcsGit, "ssh://user@example.com/foo.git", false},
+		{vcsGit, "foo://example.com/bar.git", true},
+		{vcsHg, "foo://example.com/bar.hg", false},
+		{vcsSvn, "foo://example.com/svn", false},
+		{vcsBzr, "foo://example.com/bar.bzr", false},
+	}
+
+	os.Setenv("GIT_ALLOW_PROTOCOL", "https:foo")
+	for _, test := range tests {
+		secure := test.vcs.isSecure(test.url)
+		if secure != test.secure {
+			t.Errorf("%s isSecure(%q) = %t; want %t", test.vcs, test.url, secure, test.secure)
+		}
+	}
+}
+
 func TestMatchGoImport(t *testing.T) {
 	tests := []struct {
 		imports []metaImport