1 files changed, 74 insertions, 29 deletions

diff --git a/openssl/crypto/rsa/rsa_pk1.c b/openssl/crypto/rsa/rsa_pk1.c
index 8560755f1..c2da56f6c 100644
--- a/openssl/crypto/rsa/rsa_pk1.c
+++ b/openssl/crypto/rsa/rsa_pk1.c
@@ -56,6 +56,8 @@
  * [including the GNU Public Licence.]
  */
 
+#include "constant_time_locl.h"
+
 #include <stdio.h>
 #include "cryptlib.h"
 #include <openssl/bn.h>
@@ -181,44 +183,87 @@ int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
 	     const unsigned char *from, int flen, int num)
 	{
-	int i,j;
-	const unsigned char *p;
+	int i;
+	/* |em| is the encoded message, zero-padded to exactly |num| bytes */
+	unsigned char *em = NULL;
+	unsigned int good, found_zero_byte;
+	int zero_index = 0, msg_index, mlen = -1;
 
-	p=from;
-	if ((num != (flen+1)) || (*(p++) != 02))
-		{
-		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_BLOCK_TYPE_IS_NOT_02);
-		return(-1);
-		}
-#ifdef PKCS1_CHECK
-	return(num-11);
-#endif
+        if (tlen < 0 || flen < 0)
+		return -1;
 
-	/* scan over padding data */
-	j=flen-1; /* one for type. */
-	for (i=0; i<j; i++)
-		if (*(p++) == 0) break;
+	/* PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography
+	 * Standard", section 7.2.2. */
 
-	if (i == j)
+	if (flen > num)
+		goto err;
+
+	if (num < 11)
+		goto err;
+
+	em = OPENSSL_malloc(num);
+	if (em == NULL)
 		{
-		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_NULL_BEFORE_BLOCK_MISSING);
-		return(-1);
+		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
+		return -1;
 		}
+	memset(em, 0, num);
+	/*
+	 * Always do this zero-padding copy (even when num == flen) to avoid
+	 * leaking that information. The copy still leaks some side-channel
+	 * information, but it's impossible to have a fixed  memory access
+	 * pattern since we can't read out of the bounds of |from|.
+	 *
+	 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
+	 */
+	memcpy(em + num - flen, from, flen);
 
-	if (i < 8)
+	good = constant_time_is_zero(em[0]);
+	good &= constant_time_eq(em[1], 2);
+
+	found_zero_byte = 0;
+	for (i = 2; i < num; i++)
 		{
-		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_BAD_PAD_BYTE_COUNT);
-		return(-1);
+		unsigned int equals0 = constant_time_is_zero(em[i]);
+		zero_index = constant_time_select_int(~found_zero_byte & equals0, i, zero_index);
+		found_zero_byte |= equals0;
 		}
-	i++; /* Skip over the '\0' */
-	j-=i;
-	if (j > tlen)
+
+	/*
+	 * PS must be at least 8 bytes long, and it starts two bytes into |em|.
+         * If we never found a 0-byte, then |zero_index| is 0 and the check
+	 * also fails.
+	 */
+	good &= constant_time_ge((unsigned int)(zero_index), 2 + 8);
+
+	/* Skip the zero byte. This is incorrect if we never found a zero-byte
+	 * but in this case we also do not copy the message out. */
+	msg_index = zero_index + 1;
+	mlen = num - msg_index;
+
+	/* For good measure, do this check in constant time as well; it could
+	 * leak something if |tlen| was assuming valid padding. */
+	good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen));
+
+	/*
+	 * We can't continue in constant-time because we need to copy the result
+	 * and we cannot fake its length. This unavoidably leaks timing
+	 * information at the API boundary.
+	 * TODO(emilia): this could be addressed at the call site,
+	 * see BoringSSL commit 0aa0767340baf925bda4804882aab0cb974b2d26.
+	 */
+	if (!good)
 		{
-		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_DATA_TOO_LARGE);
-		return(-1);
+		mlen = -1;
+		goto err;
 		}
-	memcpy(to,p,(unsigned int)j);
 
-	return(j);
-	}
+	memcpy(to, em + msg_index, mlen);
 
+err:
+	if (em != NULL)
+		OPENSSL_free(em);
+	if (mlen == -1)
+		RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
+	return mlen;
+	}