File 0009-rsa-rsa_ssl.c-make-RSA_padding_check_SSLv23-constant.patch of Package openssl-1_0_0.16376
From 110ef88b99f1acc6b976f2e49153734924181db2 Mon Sep 17 00:00:00 2001
From: Andy Polyakov <appro@openssl.org>
Date: Fri, 14 Sep 2018 17:24:13 +0200
Subject: [PATCH 5/5] rsa/rsa_ssl.c: make RSA_padding_check_SSLv23
constant-time.
Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
if nul delimiter is preceded by 8 consecutive 0x03 bytes.
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(cherry picked from commit 603221407ddc6404f8c417c6beadebf84449074c)
Resolved conflicts:
crypto/rsa/rsa_ssl.c
(Merged from https://github.com/openssl/openssl/pull/7737)
---
crypto/rsa/rsa_ssl.c | 134 +++++++++++++++++++++++++++++++------------
1 file changed, 97 insertions(+), 37 deletions(-)
diff --git a/crypto/rsa/rsa_ssl.c b/crypto/rsa/rsa_ssl.c
index 831f75aaf4..e9a5fe2385 100644
--- a/crypto/rsa/rsa_ssl.c
+++ b/crypto/rsa/rsa_ssl.c
@@ -61,6 +61,7 @@
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>
+#include "constant_time_locl.h"
int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
const unsigned char *from, int flen)
@@ -101,57 +102,116 @@ int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
return (1);
}
+/*
+ * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
+ * if nul delimiter is preceded by 8 consecutive 0x03 bytes. It also
+ * preserves error code reporting for backward compatibility.
+ */
int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
const unsigned char *from, int flen, int num)
{
- int i, j, k;
- 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, mask, threes_in_row;
+ int zero_index = 0, msg_index, mlen = -1, err;
- p = from;
if (flen < 10) {
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
return (-1);
}
- /* Accept even zero-padded input */
- if (flen == num) {
- if (*(p++) != 0) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_BLOCK_TYPE_IS_NOT_02);
- return -1;
- }
- flen--;
+
+ em = OPENSSL_malloc(num);
+ if (em == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
+ return -1;
}
- if ((num != (flen + 1)) || (*(p++) != 02)) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_BLOCK_TYPE_IS_NOT_02);
- return (-1);
+ /*
+ * Caller is encouraged to pass zero-padded message created with
+ * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
+ * bounds, it's impossible to have an invariant memory access pattern
+ * in case |from| was not zero-padded in advance.
+ */
+ for (from += flen, em += num, i = 0; i < num; i++) {
+ mask = ~constant_time_is_zero(flen);
+ flen -= 1 & mask;
+ from -= 1 & mask;
+ *--em = *from & mask;
}
+ from = em;
+
+ good = constant_time_is_zero(from[0]);
+ good &= constant_time_eq(from[1], 2);
+ err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
+ mask = ~good;
/* scan over padding data */
- j = flen - 1; /* one for type */
- for (i = 0; i < j; i++)
- if (*(p++) == 0)
- break;
-
- if ((i == j) || (i < 8)) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23,
- RSA_R_NULL_BEFORE_BLOCK_MISSING);
- return (-1);
- }
- for (k = -9; k < -1; k++) {
- if (p[k] != 0x03)
- break;
- }
- if (k == -1) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_SSLV3_ROLLBACK_ATTACK);
- return (-1);
+ found_zero_byte = 0;
+ threes_in_row = 0;
+ for (i = 2; i < num; i++) {
+ unsigned int equals0 = constant_time_is_zero(from[i]);
+
+ zero_index = constant_time_select_int(~found_zero_byte & equals0,
+ i, zero_index);
+ found_zero_byte |= equals0;
+
+ threes_in_row += 1 & ~found_zero_byte;
+ threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
}
- i++; /* Skip over the '\0' */
- j -= i;
- if (j > tlen) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_LARGE);
- return (-1);
+ /*
+ * PS must be at least 8 bytes long, and it starts two bytes into |from|.
+ * If we never found a 0-byte, then |zero_index| is 0 and the check
+ * also fails.
+ */
+ good &= constant_time_ge(zero_index, 2 + 8);
+ err = constant_time_select_int(mask | good, err,
+ RSA_R_NULL_BEFORE_BLOCK_MISSING);
+ mask = ~good;
+
+ good &= constant_time_lt(threes_in_row, 8);
+ err = constant_time_select_int(mask | good, err,
+ RSA_R_SSLV3_ROLLBACK_ATTACK);
+ mask = ~good;
+
+ /*
+ * 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.
+ */
+ good &= constant_time_ge(tlen, mlen);
+ err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
+
+ /*
+ * Even though we can't fake result's length, we can pretend copying
+ * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
+ * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
+ * where |mlen'| is "saturated" |mlen| value. Deducing information
+ * about failure or |mlen| would take attacker's ability to observe
+ * memory access pattern with byte granularity *as it occurs*. It
+ * should be noted that failure is indistinguishable from normal
+ * operation if |tlen| is fixed by protocol.
+ */
+ tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
+ msg_index = constant_time_select_int(good, msg_index, num - tlen);
+ mlen = num - msg_index;
+ for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
+ unsigned int equals = constant_time_eq(i, mlen);
+
+ from -= tlen & equals; /* if (i == mlen) rewind */
+ mask &= mask ^ equals; /* if (i == mlen) mask = 0 */
+ to[i] = constant_time_select_8(mask, from[i], to[i]);
}
- memcpy(to, p, (unsigned int)j);
- return (j);
+ OPENSSL_cleanse(em, num);
+ OPENSSL_free(em);
+ RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
+ err_clear_last_constant_time(1 & good);
+
+ return constant_time_select_int(good, mlen, -1);
}
--
2.20.1
