From 6555a8941bd6be5790d3b45c41de23234a8e527f Mon Sep 17 00:00:00 2001 From: Bernd Edlinger Date: Thu, 28 Feb 2019 10:08:18 +0100 Subject: [PATCH] Fix memory overrun in rsa padding check functions Backported from d7f5e5ae6d5 Fixes #8364 and #8357 Reviewed-by: Kurt Roeckx (Merged from https://github.com/openssl/openssl/pull/8438) --- crypto/rsa/rsa_oaep.c | 24 ++++++++++++------------ crypto/rsa/rsa_pk1.c | 22 +++++++++++----------- crypto/rsa/rsa_ssl.c | 33 ++++++++++++++++++--------------- 3 files changed, 41 insertions(+), 38 deletions(-) diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c index 033ea5a520..acba7f13ff 100644 --- a/crypto/rsa/rsa_oaep.c +++ b/crypto/rsa/rsa_oaep.c @@ -144,7 +144,7 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, * |num| is the length of the modulus; |flen| is the length of the * encoded message. Therefore, for any |from| that was obtained by * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, - * num < 2 * mdlen + 2 must hold for the modulus irrespective of + * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of * the ciphertext, see PKCS #1 v2.2, section 7.1.2. * This does not leak any side-channel information. */ @@ -180,17 +180,16 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, from -= 1 & mask; *--em = *from & mask; } - from = em; /* * The first byte must be zero, however we must not leak if this is * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). */ - good = constant_time_is_zero(from[0]); + good = constant_time_is_zero(em[0]); - maskedseed = from + 1; - maskeddb = from + 1 + mdlen; + maskedseed = em + 1; + maskeddb = em + 1 + mdlen; if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md)) goto cleanup; @@ -231,7 +230,7 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, mlen = dblen - msg_index; /* - * For good measure, do this check in constant tine as well. + * For good measure, do this check in constant time as well. */ good &= constant_time_ge(tlen, mlen); @@ -245,15 +244,16 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, * 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); + tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen), + dblen - mdlen - 1, 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); + for (mask = good, i = 0; i < tlen; i++) { + unsigned int equals = constant_time_eq(msg_index, dblen); - 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]); + msg_index -= tlen & equals; /* rewind at EOF */ + mask &= ~equals; /* mask = 0 at EOF */ + to[i] = constant_time_select_8(mask, db[msg_index++], to[i]); } /* diff --git a/crypto/rsa/rsa_pk1.c b/crypto/rsa/rsa_pk1.c index 074bc0a939..2c43a54e31 100644 --- a/crypto/rsa/rsa_pk1.c +++ b/crypto/rsa/rsa_pk1.c @@ -241,15 +241,14 @@ int RSA_padding_check_PKCS1_type_2(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); /* scan over padding data */ found_zero_byte = 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); @@ -257,7 +256,7 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen, } /* - * 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. */ @@ -285,15 +284,16 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen, * 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); + tlen = constant_time_select_int(constant_time_lt(num - 11, tlen), + num - 11, 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); + for (mask = good, i = 0; i < tlen; i++) { + unsigned int equals = constant_time_eq(msg_index, num); - 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]); + msg_index -= tlen & equals; /* rewind at EOF */ + mask &= ~equals; /* mask = 0 at EOF */ + to[i] = constant_time_select_8(mask, em[msg_index++], to[i]); } OPENSSL_cleanse(em, num); diff --git a/crypto/rsa/rsa_ssl.c b/crypto/rsa/rsa_ssl.c index e9a5fe2385..61751fe6f1 100644 --- a/crypto/rsa/rsa_ssl.c +++ b/crypto/rsa/rsa_ssl.c @@ -104,7 +104,7 @@ 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, @@ -116,7 +116,10 @@ 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); } @@ -138,10 +141,9 @@ 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; @@ -149,18 +151,18 @@ 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. */ @@ -169,7 +171,7 @@ 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; @@ -197,15 +199,16 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen, * 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); + tlen = constant_time_select_int(constant_time_lt(num - 11, tlen), + num - 11, 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); + for (mask = good, i = 0; i < tlen; i++) { + unsigned int equals = constant_time_eq(msg_index, num); - 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]); + msg_index -= tlen & equals; /* rewind at EOF */ + mask &= ~equals; /* mask = 0 at EOF */ + to[i] = constant_time_select_8(mask, em[msg_index++], to[i]); } OPENSSL_cleanse(em, num); -- 2.25.1