From 4535fc312b76cb5b05b6a8064c1c64d9780f55ba Mon Sep 17 00:00:00 2001
From: "Vladimir Olovyannikov via groups.io"
 <vladimir.olovyannikov=broadcom.com@groups.io>
Date: Wed, 1 Jul 2020 19:31:13 -0700
Subject: [PATCH] MdePkg: UefiFileHandleLib: fix buffer overrun in
 FileHandleReadLine()

If the size of the supplied buffer in FileHandleReadLine(), module
UefiFileHandleLib.c, was not 0, but was not enough to fit in
the line, the size is increased, and then the Buffer of the new
size is zeroed. This size is always larger than the supplied buffer size,
causing supplied buffer overrun. Fix the issue by using the
supplied buffer size in ZeroMem().

Signed-off-by: Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Message-Id: <20200702023113.10517-1-vladimir.olovyannikov@broadcom.com>
Reviewed-by: Zhiguang Liu <zhiguang.liu@intel.com>
[lersek@redhat.com: remove stray space character from subject line]
---
 MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c b/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
index 28e28e5f67..ab34e6ccd5 100644
--- a/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
+++ b/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
@@ -969,6 +969,7 @@ FileHandleReadLine(
   UINTN       CharSize;
   UINTN       CountSoFar;
   UINTN       CrCount;
+  UINTN       OldSize;
   UINT64      OriginalFilePosition;
 
   if (Handle == NULL
@@ -1039,10 +1040,11 @@ FileHandleReadLine(
   // if we ran out of space tell when...
   //
   if ((CountSoFar+1-CrCount)*sizeof(CHAR16) > *Size){
+    OldSize = *Size;
     *Size = (CountSoFar+1-CrCount)*sizeof(CHAR16);
     if (!Truncate) {
-      if (Buffer != NULL && *Size != 0) {
-        ZeroMem(Buffer, *Size);
+      if (Buffer != NULL && OldSize != 0) {
+        ZeroMem(Buffer, OldSize);
       }
       FileHandleSetPosition(Handle, OriginalFilePosition);
       return (EFI_BUFFER_TOO_SMALL);