The function StartPciDevices has a check

ASSERT (RootBridge != NULL);

but this comes into play only in DEBUG mode. In Release mode, there
is no handling if the RootBridge value is NULL and the code proceeds
to unconditionally dereference "RootBridge" which will lead to CRASH.

Hence, for safety add NULL pointer checks always and return
EFI_NOT_READY if RootBridge value is NULL which is one of the return
values as mentioned in the function description header.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4240
Signed-off-by: Ranbir Singh <Ranbir.Singh3@Dell.com>
---
MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
index 581e9075ad..f43f10325f 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
@@ -773,6 +773,11 @@ StartPciDevices (

RootBridge = GetRootBridgeByHandle (Controller);
ASSERT (RootBridge != NULL);
+
+  if (RootBridge == NULL) {
+    return EFI_NOT_READY;
+  }
+
ThisHostBridge = RootBridge->PciRootBridgeIo->ParentHandle;

CurrentLink = mPciDevicePool.ForwardLink;
--
2.36.1.windows.1