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-rw-r--r--crypto/rsa/rsa_ssl.c57
1 files changed, 30 insertions, 27 deletions
diff --git a/crypto/rsa/rsa_ssl.c b/crypto/rsa/rsa_ssl.c
index c5654595fb2f..3859128a6d80 100644
--- a/crypto/rsa/rsa_ssl.c
+++ b/crypto/rsa/rsa_ssl.c
@@ -1,5 +1,5 @@
/*
- * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
@@ -55,7 +55,7 @@ int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
/*
* 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
+ * if nul delimiter is not 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,
@@ -67,7 +67,10 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
unsigned int good, found_zero_byte, mask, threes_in_row;
int zero_index = 0, msg_index, mlen = -1, err;
- if (flen < 10) {
+ if (tlen <= 0 || flen <= 0)
+ return -1;
+
+ if (flen > num || num < 11) {
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
return -1;
}
@@ -89,10 +92,9 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
from -= 1 & mask;
*--em = *from & mask;
}
- from = em;
- good = constant_time_is_zero(from[0]);
- good &= constant_time_eq(from[1], 2);
+ good = constant_time_is_zero(em[0]);
+ good &= constant_time_eq(em[1], 2);
err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
mask = ~good;
@@ -100,18 +102,18 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
found_zero_byte = 0;
threes_in_row = 0;
for (i = 2; i < num; i++) {
- unsigned int equals0 = constant_time_is_zero(from[i]);
+ 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;
threes_in_row += 1 & ~found_zero_byte;
- threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
+ threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
}
/*
- * PS must be at least 8 bytes long, and it starts two bytes into |from|.
+ * 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.
*/
@@ -120,7 +122,7 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
RSA_R_NULL_BEFORE_BLOCK_MISSING);
mask = ~good;
- good &= constant_time_lt(threes_in_row, 8);
+ good &= constant_time_ge(threes_in_row, 8);
err = constant_time_select_int(mask | good, err,
RSA_R_SSLV3_ROLLBACK_ATTACK);
mask = ~good;
@@ -139,24 +141,25 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
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.
+ * Move the result in-place by |num|-11-|mlen| bytes to the left.
+ * Then if |good| move |mlen| bytes from |em|+11 to |to|.
+ * Otherwise leave |to| unchanged.
+ * Copy the memory back in a way that does not reveal the size of
+ * the data being copied via a timing side channel. This requires copying
+ * parts of the buffer multiple times based on the bits set in the real
+ * length. Clear bits do a non-copy with identical access pattern.
+ * The loop below has overall complexity of O(N*log(N)).
*/
- 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]);
+ tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
+ num - 11, tlen);
+ for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) {
+ mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0);
+ for (i = 11; i < num - msg_index; i++)
+ em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
+ }
+ for (i = 0; i < tlen; i++) {
+ mask = good & constant_time_lt(i, mlen);
+ to[i] = constant_time_select_8(mask, em[i + 11], to[i]);
}
OPENSSL_clear_free(em, num);