According to the UEFI Specification, data values in EFI_BLOCK_IO_MEDIA 
are read-only.
This patch introduces a local variable to avoid overwriting IoAlign and 
reduces unnecessary overallocation.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Kornel Pal <kornelpal@gmail.com>
---
  ShellPkg/Library/UefiShellDebug1CommandsLib/Dblk.c | 10 ++++++----
  1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/ShellPkg/Library/UefiShellDebug1CommandsLib/Dblk.c 
b/ShellPkg/Library/UefiShellDebug1CommandsLib/Dblk.c
index 3632ca8a7a..b2cbae84f3 100644
--- a/ShellPkg/Library/UefiShellDebug1CommandsLib/Dblk.c
+++ b/ShellPkg/Library/UefiShellDebug1CommandsLib/Dblk.c
@@ -39,6 +39,7 @@ DisplayTheBlocks(
    UINT8                     *Buffer;
    UINT8                     *OriginalBuffer;
    UINTN                     BufferSize;
+  UINT32                    IoAlign;

    ShellStatus = SHELL_SUCCESS;

@@ -53,13 +54,14 @@ DisplayTheBlocks(
    }

    BufferSize = BlockIo->Media->BlockSize * BlockCount;
-  if(BlockIo->Media->IoAlign == 0) {
-    BlockIo->Media->IoAlign = 1;
+  IoAlign    = BlockIo->Media->IoAlign;
+  if (IoAlign == 0) {
+    IoAlign = 1;
    }

    if (BufferSize > 0) {
-    OriginalBuffer = AllocateZeroPool(BufferSize + 
BlockIo->Media->IoAlign);
-    Buffer         = ALIGN_POINTER 
(OriginalBuffer,BlockIo->Media->IoAlign);
+    OriginalBuffer = AllocateZeroPool(BufferSize + IoAlign - 1);
+    Buffer         = ALIGN_POINTER (OriginalBuffer, IoAlign);
    } else {
      ShellPrintEx(-1,-1,L"  BlockSize: 0x%08x, BlockCount: 0x%08x\r\n", 
BlockIo->Media->BlockSize, BlockCount);
      OriginalBuffer = NULL;
-- 
2.15.1.windows.2

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