SecurityPkg/DxeImageVerificationLib: catch alignment overflow (CVE-20…

…19-14562)

The DxeImageVerificationHandler() function currently checks whether
"SecDataDir" has enough room for "WinCertificate->dwLength". However, for
advancing "OffSet", "WinCertificate->dwLength" is aligned to the next
multiple of 8. If "WinCertificate->dwLength" is large enough, the
alignment will return 0, and "OffSet" will be stuck at the same value.

Check whether "SecDataDir" has room left for both
"WinCertificate->dwLength" and the alignment.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Wenyi Xie <xiewenyi2@huawei.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2215
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200901091221.20948-4-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Wenyi Xie <xiewenyi2@huawei.com>
Reviewed-by: Min M Xu <min.m.xu@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c

@@ -1860,7 +1860,9 @@ DxeImageVerificationHandler (
       break;
     }
     WinCertificate = (WIN_CERTIFICATE *) (mImageBase + OffSet);
-    if (SecDataDirLeft < WinCertificate->dwLength) {
+    if (SecDataDirLeft < WinCertificate->dwLength ||
+        (SecDataDirLeft - WinCertificate->dwLength <
+         ALIGN_SIZE (WinCertificate->dwLength))) {
       break;
     }