[PATCH] MdePkg UefiLib: Check Table against NULL in ScanTableInSDT

[Star Zeng <star.zeng@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1266

af5e95215928e052445c473f1244412dadea8252 abstracted generic functions
from different modules (IntelVTdDxe, S3SaveStateDxe, PcRtc,
DpDynamicCommand and PiSmmCpuDxeSmm). Some of them (IntelVTdDxe and
PcRtc) checked Table against NULL before accessing Table->Signature,
some (S3SaveStateDxe, DpDynamicCommand and PiSmmCpuDxeSmm did not.

The ScanTableInSDT() in Acpi.c of UefiLib was mainly from
S3SaveStateDxe, so it does not check Table against NULL before
accessing Table->Signature.

This patch updates ScanTableInSDT() to check Table against NULL first
before accessing Table->Signature.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 MdePkg/Library/UefiLib/Acpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MdePkg/Library/UefiLib/Acpi.c b/MdePkg/Library/UefiLib/Acpi.c
index 4df6731ff0a4..59a828835ca0 100644
--- a/MdePkg/Library/UefiLib/Acpi.c
+++ b/MdePkg/Library/UefiLib/Acpi.c
@@ -67,7 +67,7 @@ ScanTableInSDT (
     EntryPtr = 0;
     CopyMem (&EntryPtr, (VOID *)(BasePtr + Index * TablePointerSize), TablePointerSize);
     Table = (EFI_ACPI_COMMON_HEADER *)((UINTN)(EntryPtr));
-    if (Table->Signature == Signature) {
+    if ((Table != NULL) && (Table->Signature == Signature)) {
       if (PreviousTable != NULL) {
         if (Table == PreviousTable) {
           *PreviousTableLocated = TRUE;
-- 
2.7.0.windows.1