MdePkg/SafeString: Fix potential out-of-bound memory access

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.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>

diff --git a/MdePkg/Library/BaseLib/SafeString.c b/MdePkg/Library/BaseLib/SafeString.c
index 68c33e9b7b1f1fd550244c3365be9cc17f1a9141..29310889cabbfee7f108196ffd0c3c85a6f18ee2 100644 (file)
--- a/MdePkg/Library/BaseLib/SafeString.c
+++ b/MdePkg/Library/BaseLib/SafeString.c
@@ -1,7 +1,7 @@
 /** @file\r
   Safe String functions.\r
 \r
-  Copyright (c) 2014 - 2017, Intel Corporation. All rights reserved.<BR>\r
+  Copyright (c) 2014 - 2018, Intel Corporation. All rights reserved.<BR>\r
   This program and the accompanying materials\r
   are licensed and made available under the terms and conditions of the BSD License\r
   which accompanies this distribution.  The full text of the license may be found at\r
@@ -342,7 +342,7 @@ StrnCpyS (
   //\r
   // 4. If Length is not less than DestMax, then DestMax shall be greater than StrnLenS(Source, DestMax).\r
   //\r
-  SourceLen = StrnLenS (Source, DestMax);\r
+  SourceLen = StrnLenS (Source, MIN (DestMax, Length));\r
   if (Length >= DestMax) {\r
     SAFE_STRING_CONSTRAINT_CHECK ((DestMax > SourceLen), RETURN_BUFFER_TOO_SMALL);\r
   }\r
@@ -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\r
   // character.\r
   //\r
-  while ((*Source != 0) && (SourceLen > 0)) {\r
+  while ((SourceLen > 0) && (*Source != 0)) {\r
     *(Destination++) = *(Source++);\r
     SourceLen--;\r
   }\r
@@ -551,7 +551,7 @@ StrnCatS (
   //\r
   // 5. If Length is not less than CopyLen, then CopyLen shall be greater than StrnLenS(Source, CopyLen).\r
   //\r
-  SourceLen = StrnLenS (Source, CopyLen);\r
+  SourceLen = StrnLenS (Source, MIN (CopyLen, Length));\r
   if (Length >= CopyLen) {\r
     SAFE_STRING_CONSTRAINT_CHECK ((CopyLen > SourceLen), RETURN_BUFFER_TOO_SMALL);\r
   }\r
@@ -572,7 +572,7 @@ StrnCatS (
   // a null character.\r
   //\r
   Destination = Destination + DestLen;\r
-  while ((*Source != 0) && (SourceLen > 0)) {\r
+  while ((SourceLen > 0) && (*Source != 0)) {\r
     *(Destination++) = *(Source++);\r
     SourceLen--;\r
   }\r
@@ -1916,7 +1916,7 @@ AsciiStrnCpyS (
   //\r
   // 4. If Length is not less than DestMax, then DestMax shall be greater than AsciiStrnLenS(Source, DestMax).\r
   //\r
-  SourceLen = AsciiStrnLenS (Source, DestMax);\r
+  SourceLen = AsciiStrnLenS (Source, MIN (DestMax, Length));\r
   if (Length >= DestMax) {\r
     SAFE_STRING_CONSTRAINT_CHECK ((DestMax > SourceLen), RETURN_BUFFER_TOO_SMALL);\r
   }\r
@@ -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\r
   // character.\r
   //\r
-  while ((*Source != 0) && (SourceLen > 0)) {\r
+  while ((SourceLen > 0) && (*Source != 0)) {\r
     *(Destination++) = *(Source++);\r
     SourceLen--;\r
   }\r
@@ -2115,7 +2115,7 @@ AsciiStrnCatS (
   //\r
   // 5. If Length is not less than CopyLen, then CopyLen shall be greater than AsciiStrnLenS(Source, CopyLen).\r
   //\r
-  SourceLen = AsciiStrnLenS (Source, CopyLen);\r
+  SourceLen = AsciiStrnLenS (Source, MIN (CopyLen, Length));\r
   if (Length >= CopyLen) {\r
     SAFE_STRING_CONSTRAINT_CHECK ((CopyLen > SourceLen), RETURN_BUFFER_TOO_SMALL);\r
   }\r
@@ -2136,7 +2136,7 @@ AsciiStrnCatS (
   // a null character.\r
   //\r
   Destination = Destination + DestLen;\r
-  while ((*Source != 0) && (SourceLen > 0)) {\r
+  while ((SourceLen > 0) && (*Source != 0)) {\r
     *(Destination++) = *(Source++);\r
     SourceLen--;\r
   }\r