SecurityPkg/DxeImageVerificationLib: assign WinCertificate after size check

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>

1 files 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;

     }