crypto/x509: load certs from env vars + extra locations

Add the ability to override the default file and directory from
which certificates are loaded by setting the OpenSSL compatible
environment variables: SSL_CERT_FILE, SSL_CERT_DIR.

If the variables are set the default locations are not checked.

Added new default file "/usr/local/etc/ssl/cert.pem" for FreeBSD.

Certificates in the first valid location found for both file and
directory are added, instead of only the first file location if
a valid one was found, which is consistent with OpenSSL.

Fixes #3905
Fixes #14022
Fixes #14311
Fixes #16920
Fixes #18813 - If user sets SSL_CERT_FILE.

Change-Id: Ia24fb7c1c2ffff4338b4cf214bd040326ce27bb0
Reviewed-on: https://go-review.googlesource.com/36093Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/x509/root_bsd.go

@@ -8,7 +8,8 @@ package x509
 
 // Possible certificate files; stop after finding one.
 var certFiles = []string{
-	"/usr/local/share/certs/ca-root-nss.crt", // FreeBSD/DragonFly
+	"/usr/local/etc/ssl/cert.pem",            // FreeBSD
 	"/etc/ssl/cert.pem",                      // OpenBSD
+	"/usr/local/share/certs/ca-root-nss.crt", // DragonFly
 	"/etc/openssl/certs/ca-certificates.crt", // NetBSD
 }

src/crypto/x509/root_unix.go

@@ -16,27 +16,51 @@ import (
 var certDirectories = []string{
 	"/etc/ssl/certs",               // SLES10/SLES11, https://golang.org/issue/12139
 	"/system/etc/security/cacerts", // Android
+	"/usr/local/share/certs",       // FreeBSD
+	"/etc/pki/tls/certs",           // Fedora/RHEL
+	"/etc/openssl/certs",           // NetBSD
 }
 
+const (
+	// certFileEnv is the environment variable which identifies where to locate
+	// the SSL certificate file. If set this overrides the system default.
+	certFileEnv = "SSL_CERT_FILE"
+
+	// certDirEnv is the environment variable which identifies which directory
+	// to check for SSL certificate files. If set this overrides the system default.
+	certDirEnv = "SSL_CERT_DIR"
+)
+
 func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
 	return nil, nil
 }
 
 func loadSystemRoots() (*CertPool, error) {
 	roots := NewCertPool()
+
+	files := certFiles
+	if f := os.Getenv(certFileEnv); f != "" {
+		files = []string{f}
+	}
+
 	var firstErr error
-	for _, file := range certFiles {
+	for _, file := range files {
 		data, err := ioutil.ReadFile(file)
 		if err == nil {
 			roots.AppendCertsFromPEM(data)
-			return roots, nil
+			break
 		}
 		if firstErr == nil && !os.IsNotExist(err) {
 			firstErr = err
 		}
 	}
 
-	for _, directory := range certDirectories {
+	dirs := certDirectories
+	if d := os.Getenv(certDirEnv); d != "" {
+		dirs = []string{d}
+	}
+
+	for _, directory := range dirs {
 		fis, err := ioutil.ReadDir(directory)
 		if err != nil {
 			if firstErr == nil && !os.IsNotExist(err) {
@@ -56,5 +80,9 @@ func loadSystemRoots() (*CertPool, error) {
 		}
 	}
 
+	if len(roots.certs) > 0 {
+		return roots, nil
+	}
+
 	return nil, firstErr
 }

src/crypto/x509/root_unix_test.go

+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build dragonfly freebsd linux netbsd openbsd solaris
+
+package x509
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+const (
+	testDir     = "testdata"
+	testDirCN   = "test-dir"
+	testFile    = "test-file.crt"
+	testFileCN  = "test-file"
+	testMissing = "missing"
+)
+
+func TestEnvVars(t *testing.T) {
+	testCases := []struct {
+		name    string
+		fileEnv string
+		dirEnv  string
+		files   []string
+		dirs    []string
+		cns     []string
+	}{
+		{
+			// Environment variables override the default locations preventing fall through.
+			name:    "override-defaults",
+			fileEnv: testMissing,
+			dirEnv:  testMissing,
+			files:   []string{testFile},
+			dirs:    []string{testDir},
+			cns:     nil,
+		},
+		{
+			// File environment overrides default file locations.
+			name:    "file",
+			fileEnv: testFile,
+			dirEnv:  "",
+			files:   nil,
+			dirs:    nil,
+			cns:     []string{testFileCN},
+		},
+		{
+			// Directory environment overrides default directory locations.
+			name:    "dir",
+			fileEnv: "",
+			dirEnv:  testDir,
+			files:   nil,
+			dirs:    nil,
+			cns:     []string{testDirCN},
+		},
+		{
+			// File & directory environment overrides both default locations.
+			name:    "file+dir",
+			fileEnv: testFile,
+			dirEnv:  testDir,
+			files:   nil,
+			dirs:    nil,
+			cns:     []string{testFileCN, testDirCN},
+		},
+		{
+			// Environment variable empty / unset uses default locations.
+			name:    "empty-fall-through",
+			fileEnv: "",
+			dirEnv:  "",
+			files:   []string{testFile},
+			dirs:    []string{testDir},
+			cns:     []string{testFileCN, testDirCN},
+		},
+	}
+
+	// Save old settings so we can restore before the test ends.
+	origCertFiles, origCertDirectories := certFiles, certDirectories
+	origFile, origDir := os.Getenv(certFileEnv), os.Getenv(certDirEnv)
+	defer func() {
+		certFiles = origCertFiles
+		certDirectories = origCertDirectories
+		os.Setenv(certFileEnv, origFile)
+		os.Setenv(certDirEnv, origDir)
+	}()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := os.Setenv(certFileEnv, tc.fileEnv); err != nil {
+				t.Fatalf("setenv %q failed: %v", certFileEnv, err)
+			}
+			if err := os.Setenv(certDirEnv, tc.dirEnv); err != nil {
+				t.Fatalf("setenv %q failed: %v", certDirEnv, err)
+			}
+
+			certFiles, certDirectories = tc.files, tc.dirs
+
+			r, err := loadSystemRoots()
+			if err != nil {
+				t.Fatal("unexpected failure: ", err)
+			}
+
+			if r == nil {
+				if tc.cns == nil {
+					// Expected nil
+					return
+				}
+				t.Fatal("nil roots")
+			}
+
+			for i, cn := range tc.cns {
+				if i > len(r.certs) {
+					t.Errorf("missing cert %v @ %v", cn, i)
+				} else if r.certs[i].Subject.CommonName != cn {
+					fmt.Printf("%#v\n", r.certs[0].Subject)
+					t.Errorf("unexpected cert common name %q expected %q", r.certs[i].Subject.CommonName, cn)
+				}
+			}
+
+			if len(r.certs) > len(tc.cns) {
+				t.Errorf("expected %v certs got %v", len(tc.cns), len(r.certs))
+			}
+		})
+	}
+}

src/crypto/x509/test-file.crt

+-----BEGIN CERTIFICATE-----
+MIIFbTCCA1WgAwIBAgIJAN338vEmMtLsMA0GCSqGSIb3DQEBCwUAME0xCzAJBgNV
+BAYTAlVLMRMwEQYDVQQIDApUZXN0LVN0YXRlMRUwEwYDVQQKDAxHb2xhbmcgVGVz
+dHMxEjAQBgNVBAMMCXRlc3QtZmlsZTAeFw0xNzAyMDEyMzUyMDhaFw0yNzAxMzAy
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+vQ==
+-----END CERTIFICATE-----

src/crypto/x509/testdata/test-dir.crt

+-----BEGIN CERTIFICATE-----
+MIIFazCCA1OgAwIBAgIJAL8a/lsnspOqMA0GCSqGSIb3DQEBCwUAMEwxCzAJBgNV
+BAYTAlVLMRMwEQYDVQQIDApUZXN0LVN0YXRlMRUwEwYDVQQKDAxHb2xhbmcgVGVz
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+JHyBf3GZNSWTpKY7cD8V+NnBv3UuioOVVo+XAU4LF/bYUjdRpxWADJizNtZrtFo=
+-----END CERTIFICATE-----

src/crypto/x509/x509.go

@@ -3,6 +3,10 @@
 // license that can be found in the LICENSE file.
 
 // Package x509 parses X.509-encoded keys and certificates.
+//
+// On UNIX systems the environment variables SSL_CERT_FILE and SSL_CERT_DIR
+// can be used to override the system default locations for the SSL certificate
+// file and SSL certificate files directory, respectively.
 package x509
 
 import (