x/crypto/openpgp: Limit packet recursion depth.

A carefully crafted packet can cause the packet reader to push an
infinite number of recursive packet readers. This change limits
the number of recursive parsing levels within the packet reader.

More details at:
http://mumble.net/~campbell/misc/pgp-quine
https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-4402

Fixes #10751

Change-Id: Ib4e102d85f6496e2c7feb5b9d7e5db45db6032df
Reviewed-on: https://go-review.googlesource.com/9843
Reviewed-by: Adam Langley <agl@golang.org>

openpgp/read_test.go

@@ -135,6 +135,25 @@ func TestTextSignedMessage(t *testing.T) {
 	checkSignedMessage(t, signedTextMessageHex, signedTextInput)
 }
 
+// The reader should detect "compressed quines", which are compressed
+// packets that expand into themselves and cause an infinite recursive
+// parsing loop.
+// The packet in this test case comes from Taylor R. Campbell at
+// http://mumble.net/~campbell/misc/pgp-quine/
+func TestCampbellQuine(t *testing.T) {
+	md, err := ReadMessage(readerFromHex(campbellQuine), nil, nil, nil)
+	if md != nil {
+		t.Errorf("Reading a compressed quine should not return any data: %#v", md)
+	}
+	structural, ok := err.(errors.StructuralError)
+	if !ok {
+		t.Fatalf("Unexpected class of error: %T", err)
+	}
+	if !strings.Contains(string(structural), "too many layers of packets") {
+		t.Fatalf("Unexpected error: %s", err)
+	}
+}
+
 var signedEncryptedMessageTests = []struct {
 	keyRingHex       string
 	messageHex       string
@@ -440,3 +459,5 @@ const dsaKeyWithSHA512 = `9901a2044f04b07f110400db244efecc7316553ee08d179972aab8
 const unknownHashFunctionHex = `8a00000040040001990006050253863c24000a09103b4fe6acc0b21f32ffff01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101`
 
 const missingHashFunctionHex = `8a00000040040001030006050253863c24000a09103b4fe6acc0b21f32ffff01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101`
+
+const campbellQuine = `a0b001000300fcffa0b001000d00f2ff000300fcffa0b001000d00f2ff8270a01c00000500faff8270a01c00000500faff000500faff001400ebff8270a01c00000500faff000500faff001400ebff428821c400001400ebff428821c400001400ebff428821c400001400ebff428821c400001400ebff428821c400000000ffff000000ffff000b00f4ff428821c400000000ffff000000ffff000b00f4ff0233214c40000100feff000233214c40000100feff0000`