Fix a memory leak in RSA_padding_add_PKCS1_OAEP_mgf1

Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NMatt Caswell <matt@openssl.org>
GH: #2140

crypto/rsa/rsa_oaep.c

@@ -91,17 +91,21 @@ int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
     }
 
     if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
-        return 0;
+        goto err;
     for (i = 0; i < emlen - mdlen; i++)
         db[i] ^= dbmask[i];
 
     if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
-        return 0;
+        goto err;
     for (i = 0; i < mdlen; i++)
         seed[i] ^= seedmask[i];
 
     OPENSSL_free(dbmask);
     return 1;
+
+ err:
+    OPENSSL_free(dbmask);
+    return 0;
 }
 
 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,