[release-branch.go1.12] all: merge release-branch.go1.12-security into release-branch.go1.12

Change-Id: Ic8ed07ad2c77042a67d7e1d4e9c0d5953610cf07

6 files changed, 34 insertions, 11 deletions

diff --git a/VERSION b/VERSION
index b115ecfa6a..33bccfc8ee 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-go1.12.15
\ No newline at end of file
+go1.12.16
\ No newline at end of file
diff --git a/doc/devel/release.html b/doc/devel/release.html
index 487367c35f..38a9040d5e 100644
--- a/doc/devel/release.html
+++ b/doc/devel/release.html
@@ -139,6 +139,13 @@ the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.12.15+label%3
 1.12.15 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.12.16 (released 2020/01/28) includes two security fixes to
+the <code>crypto/x509</code> package. See the
+<a href="https://github.com/golang/go/issues?q=milestone%3AGo1.12.16+label%3ACherryPickApproved">Go
+1.12.16 milestone</a> on our issue tracker for details.
+</p>
+
 <h2 id="go1.11">go1.11 (released 2018/08/24)</h2>
 
 <p>
diff --git a/src/crypto/x509/root_windows.go b/src/crypto/x509/root_windows.go
index 74d395df70..3da3d06e73 100644
--- a/src/crypto/x509/root_windows.go
+++ b/src/crypto/x509/root_windows.go
@@ -219,10 +219,26 @@ func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate
 	if err != nil {
 		return nil, err
 	}
+	if len(chain) < 1 {
+		return nil, errors.New("x509: internal error: system verifier returned an empty chain")
+	}
 
-	chains = append(chains, chain)
+	// Mitigate CVE-2020-0601, where the Windows system verifier might be
+	// tricked into using custom curve parameters for a trusted root, by
+	// double-checking all ECDSA signatures. If the system was tricked into
+	// using spoofed parameters, the signature will be invalid for the correct
+	// ones we parsed. (We don't support custom curves ourselves.)
+	for i, parent := range chain[1:] {
+		if parent.PublicKeyAlgorithm != ECDSA {
+			continue
+		}
+		if err := parent.CheckSignature(chain[i].SignatureAlgorithm,
+			chain[i].RawTBSCertificate, chain[i].Signature); err != nil {
+			return nil, err
+		}
+	}
 
-	return chains, nil
+	return [][]*Certificate{chain}, nil
 }
 
 func loadSystemRoots() (*CertPool, error) {
diff --git a/src/internal/x/crypto/cryptobyte/asn1.go b/src/internal/x/crypto/cryptobyte/asn1.go
index 2d40680ddd..758ac3a649 100644
--- a/src/internal/x/crypto/cryptobyte/asn1.go
+++ b/src/internal/x/crypto/cryptobyte/asn1.go
@@ -470,7 +470,8 @@ func (s *String) ReadASN1GeneralizedTime(out *time.Time) bool {
 // It reports whether the read was successful.
 func (s *String) ReadASN1BitString(out *encoding_asn1.BitString) bool {
 	var bytes String
-	if !s.ReadASN1(&bytes, asn1.BIT_STRING) || len(bytes) == 0 {
+	if !s.ReadASN1(&bytes, asn1.BIT_STRING) || len(bytes) == 0 ||
+		len(bytes)*8/8 != len(bytes) {
 		return false
 	}
 
@@ -740,7 +741,7 @@ func (s *String) readASN1(out *String, outTag *asn1.Tag, skipHeader bool) bool {
 		length = headerLen + len32
 	}
 
-	if uint32(int(length)) != length || !s.ReadBytes((*[]byte)(out), int(length)) {
+	if int(length) < 0 || !s.ReadBytes((*[]byte)(out), int(length)) {
 		return false
 	}
 	if skipHeader && !out.Skip(int(headerLen)) {
diff --git a/src/internal/x/crypto/cryptobyte/asn1_test.go b/src/internal/x/crypto/cryptobyte/asn1_test.go
index ca28e3bcfb..f90d768edb 100644
--- a/src/internal/x/crypto/cryptobyte/asn1_test.go
+++ b/src/internal/x/crypto/cryptobyte/asn1_test.go
@@ -31,6 +31,10 @@ var readASN1TestData = []readASN1Test{
 	{"non-minimal length", append([]byte{0x30, 0x82, 0, 0x80}, make([]byte, 0x80)...), 0x30, false, nil},
 	{"invalid tag", []byte{0xa1, 3, 0x4, 1, 1}, 31, false, nil},
 	{"high tag", []byte{0x1f, 0x81, 0x80, 0x01, 2, 1, 2}, 0xff /* actually 0x4001, but tag is uint8 */, false, nil},
+	{"2**31 - 1 length", []byte{0x30, 0x84, 0x7f, 0xff, 0xff, 0xff}, 0x30, false, nil},
+	{"2**32 - 1 length", []byte{0x30, 0x84, 0xff, 0xff, 0xff, 0xff}, 0x30, false, nil},
+	{"2**63 - 1 length", []byte{0x30, 0x88, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}, 0x30, false, nil},
+	{"2**64 - 1 length", []byte{0x30, 0x88, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}, 0x30, false, nil},
 }
 
 func TestReadASN1(t *testing.T) {
diff --git a/src/internal/x/crypto/cryptobyte/string.go b/src/internal/x/crypto/cryptobyte/string.go
index bd2ed2e207..a3ecf63828 100644
--- a/src/internal/x/crypto/cryptobyte/string.go
+++ b/src/internal/x/crypto/cryptobyte/string.go
@@ -24,7 +24,7 @@ type String []byte
 // read advances a String by n bytes and returns them. If less than n bytes
 // remain, it returns nil.
 func (s *String) read(n int) []byte {
-	if len(*s) < n {
+	if len(*s) < n || n < 0 {
 		return nil
 	}
 	v := (*s)[:n]
@@ -105,11 +105,6 @@ func (s *String) readLengthPrefixed(lenLen int, outChild *String) bool {
 		length = length << 8
 		length = length | uint32(b)
 	}
-	if int(length) < 0 {
-		// This currently cannot overflow because we read uint24 at most, but check
-		// anyway in case that changes in the future.
-		return false
-	}
 	v := s.read(int(length))
 	if v == nil {
 		return false