[CHERRY-PICK] MdeModulePkg/DxeCapsuleLibFmp: Check for NULL in IsValidCapsuleHeader

[zurcher]

Description

Add a NULL check in IsValidCapsuleHeader before dereferencing CapsuleHeader

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?
• Backport to release branch?

How This Was Tested

Published HOB with EFI_HOB_TYPE_UEFI_CAPSULE and BaseAddress = 0.
Confirmed IsValidCapsuleHeader returned FALSE instead of crashing.

Integration Instructions

N/A

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (dev/202502@8264a11). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c	0.00%	4 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev/202502    #1290   +/-   ##
=============================================
  Coverage              ?    0.64%           
=============================================
  Files                 ?      614           
  Lines                 ?   222504           
  Branches              ?      370           
=============================================
  Hits                  ?     1432           
  Misses                ?   221059           
  Partials              ?       13           

Flag	Coverage Δ
MdeModulePkg	0.64% <0.00%> (?)

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[zurcher]

Build failure is not in my change:

ERROR - Compiler #error from /__w/1/s/UnitTestFrameworkPkg/Library/Posix/MemoryAllocationLibPosix/MemoryAllocationLibPosix.c variable ‘Length’ set but not used [-Werror=unused-but-set-variable]

[zurcher]

Test failure:

Address 0x7f78a4c0b078 is located in stack of thread T0 at offset 120 in frame
    #0 0x40318f in HostTestRecordAssertion /__w/1/s/MdeModulePkg/Universal/Variable/RuntimeDxe/RuntimeDxeUnitTest/SctShim.c:200

  This frame has 5 object(s):
    [32, 52) 'AssertionType' (line 204)
    [96, 120) 'Marker' (line 201) <== Memory access at offset 120 overflows this variable
    [160, 2208) 'AssertionDetail' (line 203)
    [2336, 2352) 'EventId' (line 173)
    [2368, 3392) 'AsciiBuffer' (line 202)
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /__w/1/s/MdePkg/Library/BasePrintLib/PrintLibInternal.c:1037 in BasePrintLibSPrintMarker