File 0008-rsa-rsa_oaep.c-remove-memcpy-calls-from-RSA_padding_.patch of Package compat-openssl098.29205
From b29b91bc7ea8dfe47d873d7953175c57556a4488 Mon Sep 17 00:00:00 2001
From: Andy Polyakov <appro@openssl.org>
Date: Thu, 6 Sep 2018 21:54:23 +0200
Subject: [PATCH 4/5] rsa/rsa_oaep.c: remove memcpy calls from
RSA_padding_check_PKCS1_OAEP.
And make RSAErr call unconditional.
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(cherry picked from commit 75f5e944be97f28867e7c489823c889d89d0bd06)
Resolved conflicts:
crypto/rsa/rsa_oaep.c
(Merged from https://github.com/openssl/openssl/pull/7737)
---
crypto/rsa/rsa_oaep.c | 96 +++++++++++++++++++++++++------------------
1 file changed, 56 insertions(+), 40 deletions(-)
Index: openssl-1.0.1i/crypto/rsa/rsa_oaep.c
===================================================================
--- openssl-1.0.1i.orig/crypto/rsa/rsa_oaep.c
+++ openssl-1.0.1i/crypto/rsa/rsa_oaep.c
@@ -121,7 +121,7 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
const EVP_MD *md, const EVP_MD *mgf1md)
{
int i, dblen, mlen = -1, one_index = 0, msg_index;
- unsigned int good, found_one_byte;
+ unsigned int good = 0, found_one_byte, mask;
const unsigned char *maskedseed, *maskeddb;
/* |em| is the encoded message, zero-padded to exactly |num| bytes:
* em = Y || maskedSeed || maskedDB */
@@ -146,8 +146,11 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
* the ciphertext, see PKCS #1 v2.2, section 7.1.2.
* This does not leak any side-channel information.
*/
- if (num < flen || num < 2 * mdlen + 2)
- goto decoding_err;
+ if (num < flen || num < 2 * mdlen + 2) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+ RSA_R_OAEP_DECODING_ERROR);
+ return -1;
+ }
dblen = num - mdlen - 1;
db = OPENSSL_malloc(dblen);
@@ -156,26 +159,25 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
goto cleanup;
}
- if (flen != num) {
- em = OPENSSL_malloc(num);
- if (em == NULL) {
+ em = OPENSSL_malloc(num);
+ if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
ERR_R_MALLOC_FAILURE);
goto cleanup;
- }
-
- /*
- * Caller is encouraged to pass zero-padded message created with
- * BN_bn2binpad, but if it doesn't, we do this zero-padding copy
- * 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|.
- */
- memset(em, 0, num);
- memcpy(em + num - flen, from, flen);
- from = em;
}
+ /*
+ * 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;
/*
* The first byte must be zero, however we must not leak if this is
@@ -221,31 +223,46 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
* so plaintext-awareness ensures timing side-channels are no longer a
* concern.
*/
- if (!good)
- goto decoding_err;
msg_index = one_index + 1;
mlen = dblen - msg_index;
- if (tlen < mlen)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
- mlen = -1;
- }
- else
- {
- memcpy(to, db + msg_index, mlen);
- goto cleanup;
- }
+ /*
+ * For good measure, do this check in constant tine as well.
+ */
+ good &= constant_time_ge(tlen, mlen);
+ /*
+ * Even though we can't fake result's length, we can pretend copying
+ * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |dblen|
+ * 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(dblen, tlen), dblen, tlen);
+ msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
+ mlen = dblen - msg_index;
+ for (from = db + msg_index, mask = good, i = 0; i < tlen; i++) {
+ unsigned int equals = constant_time_eq(i, mlen);
+ from -= dblen & equals; /* if (i == dblen) rewind */
+ mask &= mask ^ equals; /* if (i == dblen) mask = 0 */
+ to[i] = constant_time_select_8(mask, from[i], to[i]);
+ }
-decoding_err:
/* To avoid chosen ciphertext attacks, the error message should not reveal
* which kind of decoding error happened. */
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_OAEP_DECODING_ERROR);
+ err_clear_last_constant_time(1 & good);
cleanup:
- if (db != NULL) OPENSSL_free(db);
- if (em != NULL) OPENSSL_free(em);
- return mlen;
+ OPENSSL_cleanse(seed, sizeof(seed));
+ OPENSSL_cleanse(db, dblen);
+ OPENSSL_free(db);
+ OPENSSL_cleanse(em, num);
+ OPENSSL_free(em);
+
+ return constant_time_select_int(good, mlen, -1);
}
int PKCS1_MGF1(unsigned char *mask, long len,
