From a7632e913c1c106f436aefd5e76c394249c383a8 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Tue, 1 Sep 2020 11:12:20 +0200
Subject: [PATCH 3/4] SecurityPkg/DxeImageVerificationLib: assign
 WinCertificate after size check
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Currently the (SecDataDirLeft <= sizeof (WIN_CERTIFICATE)) check only
guards the de-referencing of the "WinCertificate" pointer. It does not
guard the calculation of the pointer itself:

  WinCertificate = (WIN_CERTIFICATE *) (mImageBase + OffSet);

This is wrong; if we don't know for sure that we have enough room for a
WIN_CERTIFICATE, then even creating such a pointer, not just
de-referencing it, may invoke undefined behavior.

Move the pointer calculation after the size check.

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: <20200901091221.20948-3-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>
---
 .../DxeImageVerificationLib/DxeImageVerificationLib.c     | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
index 377feebb20..100739eb3e 100644
--- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
+++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
@@ -1855,10 +1855,12 @@ DxeImageVerificationHandler (
   for (OffSet = SecDataDir->VirtualAddress;
        OffSet < SecDataDirEnd;
        OffSet += (WinCertificate->dwLength + ALIGN_SIZE (WinCertificate->dwLength))) {
-    WinCertificate = (WIN_CERTIFICATE *) (mImageBase + OffSet);
     SecDataDirLeft = SecDataDirEnd - OffSet;
-    if (SecDataDirLeft <= sizeof (WIN_CERTIFICATE) ||
-        SecDataDirLeft < WinCertificate->dwLength) {
+    if (SecDataDirLeft <= sizeof (WIN_CERTIFICATE)) {
+      break;
+    }
+    WinCertificate = (WIN_CERTIFICATE *) (mImageBase + OffSet);
+    if (SecDataDirLeft < WinCertificate->dwLength) {
       break;
     }
 
-- 
2.27.0

