Fix two invalid memory reads in RSA OAEP mode.

Submitted by: Ivan Nestlerode <inestlerode@us.ibm.com>
Reviewed by: steve

diff --git a/CHANGES b/CHANGES
index 910fcb36eb0ff1b41e6757743f87f6d1a3fc83f8..3eee60b0bb7fec554057733686d2811279b535aa 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,14 @@
 
  Changes between 0.9.8g and 0.9.8h  [xx XXX xxxx]
 
+  *) RSA OAEP patches to fix two separate invalid memory reads.
+     The first one involves inputs when 'lzero' is greater than
+     'SHA_DIGEST_LENGTH' (it would read about SHA_DIGEST_LENGTH bytes
+     before the beginning of from). The second one involves inputs where
+     the 'db' section contains nothing but zeroes (there is a one-byte
+     invalid read after the end of 'db').
+     [Ivan Nesterlode <inestlerode@us.ibm.com>]
+
   *) Partial backport from 0.9.9-dev:
 
      Introduce bn_mul_mont (dedicated Montgomery multiplication

diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c
index 45d6f6ef8a5eaa5435cc3e313cc7415ab1b405ff..3652677a99822b9cd47b9354bc0ba6366e3a2fc7 100644 (file)
--- a/crypto/rsa/rsa_oaep.c
+++ b/crypto/rsa/rsa_oaep.c
@@ -96,6 +96,7 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
        const unsigned char *maskeddb;
        int lzero;
        unsigned char *db = NULL, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
+       unsigned char *padded_from;
        int bad = 0;
 
        if (--num < 2 * SHA_DIGEST_LENGTH + 1)
@@ -106,8 +107,6 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
        lzero = num - flen;
        if (lzero < 0)
                {
-               /* lzero == -1 */
-
                /* signalling this error immediately after detection might allow
                 * for side-channel attacks (e.g. timing if 'plen' is huge
                 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA Optimal
@@ -115,20 +114,28 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
                 * so we use a 'bad' flag */
                bad = 1;
                lzero = 0;
+               flen = num; /* don't overflow the memcpy to padded_from */
                }
-       maskeddb = from - lzero + SHA_DIGEST_LENGTH;
 
        dblen = num - SHA_DIGEST_LENGTH;
-       db = OPENSSL_malloc(dblen);
+       db = OPENSSL_malloc(dblen + num);
        if (db == NULL)
                {
                RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
                return -1;
                }
 
+       /* Always do this zero-padding copy (even when lzero == 0)
+        * to avoid leaking timing info about the value of lzero. */
+       padded_from = db + dblen;
+       memset(padded_from, 0, lzero);
+       memcpy(padded_from + lzero, from, flen);
+
+       maskeddb = padded_from + SHA_DIGEST_LENGTH;
+
        MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen);
-       for (i = lzero; i < SHA_DIGEST_LENGTH; i++)
-               seed[i] ^= from[i - lzero];
+       for (i = 0; i < SHA_DIGEST_LENGTH; i++)
+               seed[i] ^= padded_from[i];
   
        MGF1(db, dblen, seed, SHA_DIGEST_LENGTH);
        for (i = 0; i < dblen; i++)
@@ -143,13 +150,13 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
                for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
                        if (db[i] != 0x00)
                                break;
-               if (db[i] != 0x01 || i++ >= dblen)
+               if (i == dblen || db[i] != 0x01)
                        goto decoding_err;
                else
                        {
                        /* everything looks OK */
 
-                       mlen = dblen - i;
+                       mlen = dblen - ++i;
                        if (tlen < mlen)
                                {
                                RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);