CryptoPkg/BaseCryptLib: fix NULL dereference (CVE-2019-14584)

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1914

AuthenticodeVerify() calls OpenSSLs d2i_PKCS7() API to parse asn encoded
signed authenticode pkcs#7 data. when this successfully returns, a type
check is done by calling PKCS7_type_is_signed() and then
Pkcs7->d.sign->contents->type is used. It is possible to construct an asn1
blob that successfully decodes and have d2i_PKCS7() return a valid pointer
and have PKCS7_type_is_signed() also return success  but have Pkcs7->d.sign
be a NULL pointer.

Looking at how PKCS7_verify() [inside of OpenSSL] implements checking for
pkcs7 structs it does the following:
- call PKCS7_type_is_signed()
- call PKCS7_get_detached()
Looking into how PKCS7_get_detatched() is implemented, it checks to see if
p7->d.sign is NULL or if p7->d.sign->contents->d.ptr is NULL.

As such, the fix is to do the same as OpenSSL after calling d2i_PKCS7().
- Add call to PKS7_get_detached() to existing error handling

Cc: Xiaoyu Lu <xiaoyux.lu@intel.com>
Cc: Guomin Jiang <guomin.jiang@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>

CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c

@@ -9,7 +9,7 @@
   AuthenticodeVerify() will get PE/COFF Authenticode and will do basic check for
   data structure.
 
-Copyright (c) 2011 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2011 - 2020, Intel Corporation. All rights reserved.<BR>
 SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -100,7 +100,7 @@ AuthenticodeVerify (
   //
   // Check if it's PKCS#7 Signed Data (for Authenticode Scenario)
   //
-  if (!PKCS7_type_is_signed (Pkcs7)) {
+  if (!PKCS7_type_is_signed (Pkcs7) || PKCS7_get_detached (Pkcs7)) {
     goto _Exit;
   }