Check that we have enough padding characters.

Reviewed-by: Emilia Käsper <emilia@openssl.org>

CVE-2016-2107

MR: #2572

crypto/evp/e_aes_cbc_hmac_sha1.c

diff --git a/crypto/evp/e_aes_cbc_hmac_sha1.c b/crypto/evp/e_aes_cbc_hmac_sha1.c
index 394a380..2d5131f 100644
--- a/crypto/evp/e_aes_cbc_hmac_sha1.c
+++ b/crypto/evp/e_aes_cbc_hmac_sha1.c
@@ -59,6 +59,7 @@
 #include <openssl/rand.h>
 #include "modes_lcl.h"
 #include "internal/evp_int.h"
+#include "internal/constant_time_locl.h"
 
 #ifndef EVP_CIPH_FLAG_AEAD_CIPHER
 # define EVP_CIPH_FLAG_AEAD_CIPHER       0x200000
@@ -583,6 +584,8 @@
             maxpad |= (255 - maxpad) >> (sizeof(maxpad) * 8 - 8);
             maxpad &= 255;
 
+            ret &= constant_time_ge(maxpad, pad);
+
             inp_len = len - (SHA_DIGEST_LENGTH + pad + 1);
             mask = (0 - ((inp_len - len) >> (sizeof(inp_len) * 8 - 1)));
             inp_len &= mask;

crypto/evp/e_aes_cbc_hmac_sha256.c

diff --git a/crypto/evp/e_aes_cbc_hmac_sha256.c b/crypto/evp/e_aes_cbc_hmac_sha256.c
index 956cd58a..3ac59ab 100644
--- a/crypto/evp/e_aes_cbc_hmac_sha256.c
+++ b/crypto/evp/e_aes_cbc_hmac_sha256.c
@@ -59,6 +59,7 @@
 #include <openssl/sha.h>
 #include <openssl/rand.h>
 #include "modes_lcl.h"
+#include "internal/constant_time_locl.h"
 #include "internal/evp_int.h"
 
 #ifndef EVP_CIPH_FLAG_AEAD_CIPHER
@@ -594,6 +595,8 @@
             maxpad |= (255 - maxpad) >> (sizeof(maxpad) * 8 - 8);
             maxpad &= 255;
 
+            ret &= constant_time_ge(maxpad, pad);
+
             inp_len = len - (SHA256_DIGEST_LENGTH + pad + 1);
             mask = (0 - ((inp_len - len) >> (sizeof(inp_len) * 8 - 1)));
             inp_len &= mask;