Check that we have enough padding characters.

Reviewed-by: Emilia Käsper <emilia@openssl.org>
CVE-2016-2107

MR: #2572

(cherry-picked from commit 4159f311671cf3bac03815e5de44681eb758304a)

Bug: 28550804
Change-Id: Ia43cfe32f8930112eb38dbef614c96db43b30c27

Author: kroeckx

crypto/evp/e_aes_cbc_hmac_sha1.c

@@ -59,6 +59,7 @@
 #include <openssl/aes.h>
 #include <openssl/sha.h>
 #include "evp_locl.h"
+#include "constant_time_locl.h"
 
 #ifndef EVP_CIPH_FLAG_AEAD_CIPHER
 #define EVP_CIPH_FLAG_AEAD_CIPHER	0x200000
@@ -278,6 +279,8 @@ static int aesni_cbc_hmac_sha1_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
 			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;