Add additional DigestInfo checks.

Reencode DigestInto in DER and check against the original: this
will reject any improperly encoded DigestInfo structures.

Note: this is a precautionary measure, there is no known attack
which can exploit this.

Thanks to Brian Smith for reporting this issue.
Reviewed-by: NTim Hudson <tjh@openssl.org>

CHANGES

@@ -627,6 +627,16 @@
 
  Changes between 1.0.1g and 1.0.1h [5 Jun 2014]
 
+  *) Add additional DigestInfo checks.
+ 
+     Reencode DigestInto in DER and check against the original: this
+     will reject any improperly encoded DigestInfo structures.
+
+     Note: this is a precautionary measure OpenSSL and no attacks
+     are currently known.
+
+     [Steve Henson]
+
   *) Fix for SSL/TLS MITM flaw. An attacker using a carefully crafted
      handshake can force the use of weak keying material in OpenSSL
      SSL/TLS clients and servers.

crypto/rsa/rsa_sign.c

@@ -143,6 +143,25 @@ int RSA_sign(int type, const unsigned char *m, unsigned int m_len,
 	return(ret);
 	}
 
+/*
+ * Check DigestInfo structure does not contain extraneous data by reencoding
+ * using DER and checking encoding against original. 
+ */
+static int rsa_check_digestinfo(X509_SIG *sig, const unsigned char *dinfo, int dinfolen)
+	{
+	unsigned char *der = NULL;
+	int derlen;
+	int ret = 0;
+	derlen = i2d_X509_SIG(sig, &der);
+	if (derlen <= 0)
+		return 0;
+	if (derlen == dinfolen && !memcmp(dinfo, der, derlen))
+		ret = 1;
+	OPENSSL_cleanse(der, derlen);
+	OPENSSL_free(der);
+	return ret;
+	}
+
 int int_rsa_verify(int dtype, const unsigned char *m,
 			  unsigned int m_len,
 			  unsigned char *rm, size_t *prm_len,
@@ -211,7 +230,7 @@ int int_rsa_verify(int dtype, const unsigned char *m,
 		if (sig == NULL) goto err;
 
 		/* Excess data can be used to create forgeries */
-		if(p != s+i)
+		if(p != s+i || !rsa_check_digestinfo(sig, s, i))
 			{
 			RSAerr(RSA_F_INT_RSA_VERIFY,RSA_R_BAD_SIGNATURE);
 			goto err;