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Fix memory overrun in rsa padding check functions
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Backported from d7f5e5a

Fixes openssl#8364 and openssl#8357

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
(Merged from openssl#8438)
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@bernd-edlinger
bernd-edlinger committed Mar 7, 2019
1 parent d5e37fc commit 6555a89
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Showing 3 changed files with 41 additions and 38 deletions.
24 changes: 12 additions & 12 deletions crypto/rsa/rsa_oaep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
*/
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);

Expand All @@ -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]);
}

/*
Expand Down
22 changes: 11 additions & 11 deletions crypto/rsa/rsa_pk1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -241,23 +241,22 @@ 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);
found_zero_byte |= equals0;
}

/*
* 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.
*/
Expand Down Expand Up @@ -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);
Expand Down
33 changes: 18 additions & 15 deletions crypto/rsa/rsa_ssl.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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);
}
Expand All @@ -138,29 +141,28 @@ 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;

/* scan over padding data */
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.
*/
Expand All @@ -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;
Expand Down Expand Up @@ -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);
Expand Down

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