Today's implementation of [Ascii]StrnCpyS/[Ascii]StrnCatS calls
StrnLenS () to get the length of source string but supplies the
destination buffer size as max size.
It's a bug that may cause out-of-bound memory access.
For example:
  StrnCpyS (Dest[10], 10, "hello", 6)
  -> StrnLenS ("hello", 10) //< cause out-of bound memory access

In a pool guard enabled environment, when using shell to edit an
existing file which contains empty line, the page fault is met.

The patch fixes the four library functions to avoid such
out-of-bound memory access.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu...@intel.com>
Cc: Jiewen Yao <jiewen....@intel.com>
Cc: Liming Gao <liming....@intel.com>
Cc: Jian J Wang <jian.j.w...@intel.com>
---
 MdePkg/Library/BaseLib/SafeString.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/MdePkg/Library/BaseLib/SafeString.c 
b/MdePkg/Library/BaseLib/SafeString.c
index 68c33e9b7b..29310889ca 100644
--- a/MdePkg/Library/BaseLib/SafeString.c
+++ b/MdePkg/Library/BaseLib/SafeString.c
@@ -1,7 +1,7 @@
 /** @file
   Safe String functions.
 
-  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD 
License
   which accompanies this distribution.  The full text of the license may be 
found at
@@ -342,7 +342,7 @@ StrnCpyS (
   //
   // 4. If Length is not less than DestMax, then DestMax shall be greater than 
StrnLenS(Source, DestMax).
   //
-  SourceLen = StrnLenS (Source, DestMax);
+  SourceLen = StrnLenS (Source, MIN (DestMax, Length));
   if (Length >= DestMax) {
     SAFE_STRING_CONSTRAINT_CHECK ((DestMax > SourceLen), 
RETURN_BUFFER_TOO_SMALL);
   }
@@ -361,7 +361,7 @@ StrnCpyS (
   // pointed to by Destination. If no null character was copied from Source, 
then Destination[Length] is set to a null
   // character.
   //
-  while ((*Source != 0) && (SourceLen > 0)) {
+  while ((SourceLen > 0) && (*Source != 0)) {
     *(Destination++) = *(Source++);
     SourceLen--;
   }
@@ -551,7 +551,7 @@ StrnCatS (
   //
   // 5. If Length is not less than CopyLen, then CopyLen shall be greater than 
StrnLenS(Source, CopyLen).
   //
-  SourceLen = StrnLenS (Source, CopyLen);
+  SourceLen = StrnLenS (Source, MIN (CopyLen, Length));
   if (Length >= CopyLen) {
     SAFE_STRING_CONSTRAINT_CHECK ((CopyLen > SourceLen), 
RETURN_BUFFER_TOO_SMALL);
   }
@@ -572,7 +572,7 @@ StrnCatS (
   // a null character.
   //
   Destination = Destination + DestLen;
-  while ((*Source != 0) && (SourceLen > 0)) {
+  while ((SourceLen > 0) && (*Source != 0)) {
     *(Destination++) = *(Source++);
     SourceLen--;
   }
@@ -1916,7 +1916,7 @@ AsciiStrnCpyS (
   //
   // 4. If Length is not less than DestMax, then DestMax shall be greater than 
AsciiStrnLenS(Source, DestMax).
   //
-  SourceLen = AsciiStrnLenS (Source, DestMax);
+  SourceLen = AsciiStrnLenS (Source, MIN (DestMax, Length));
   if (Length >= DestMax) {
     SAFE_STRING_CONSTRAINT_CHECK ((DestMax > SourceLen), 
RETURN_BUFFER_TOO_SMALL);
   }
@@ -1935,7 +1935,7 @@ AsciiStrnCpyS (
   // pointed to by Destination. If no null character was copied from Source, 
then Destination[Length] is set to a null
   // character.
   //
-  while ((*Source != 0) && (SourceLen > 0)) {
+  while ((SourceLen > 0) && (*Source != 0)) {
     *(Destination++) = *(Source++);
     SourceLen--;
   }
@@ -2115,7 +2115,7 @@ AsciiStrnCatS (
   //
   // 5. If Length is not less than CopyLen, then CopyLen shall be greater than 
AsciiStrnLenS(Source, CopyLen).
   //
-  SourceLen = AsciiStrnLenS (Source, CopyLen);
+  SourceLen = AsciiStrnLenS (Source, MIN (CopyLen, Length));
   if (Length >= CopyLen) {
     SAFE_STRING_CONSTRAINT_CHECK ((CopyLen > SourceLen), 
RETURN_BUFFER_TOO_SMALL);
   }
@@ -2136,7 +2136,7 @@ AsciiStrnCatS (
   // a null character.
   //
   Destination = Destination + DestLen;
-  while ((*Source != 0) && (SourceLen > 0)) {
+  while ((SourceLen > 0) && (*Source != 0)) {
     *(Destination++) = *(Source++);
     SourceLen--;
   }
-- 
2.16.1.windows.1

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