[PATCH v1 1/1] MdePkg : UefiFileHandleLib: fix buffer overrun in FileHandleReadLine()

["Vladimir Olovyannikov" <vladimir.olovyannikov@broadcom.com>]

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>
---
 MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c b/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
index 28e28e5f67d5..4bc9fabb6c74 100644
--- a/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
+++ b/MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.c
@@ -1039,10 +1039,13 @@ FileHandleReadLine(
   // if we ran out of space tell when...
   //
   if ((CountSoFar+1-CrCount)*sizeof(CHAR16) > *Size){
+    UINTN OldSize;
+
+    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);
-- 
2.26.2.266.ge870325ee8