cmHexFileConverter: Avoid stack buffer overflow

Prevent overflow on maliciously-crafted Motorola S1 record files which
have a maximum line length over the 256-byte maximum.

Source/cmHexFileConverter.cxx

@@ -45,6 +45,10 @@ static bool OutputBin(FILE* file, char const* buf, unsigned int startIndex,
       success = false;
       break;
     }
+    if (outBufCount >= sizeof(outBuf)) {
+      success = false;
+      break;
+    }
     outBuf[outBufCount] = static_cast<char>(convertedByte & 0xff);
     outBufCount++;
   }

Tests/StringFileTest/CMakeLists.txt

@@ -55,6 +55,10 @@ else()
     "file(STRINGS) incorrectly read from srec file [${infile_strings}]")
 endif()
 
+# this file is crafted to contain the maximum line length and trigger a buffer
+# overflow
+file(STRINGS "${CMAKE_CURRENT_SOURCE_DIR}/s1-max-length.srec" infile_strings)
+
 #this file has utf-8 content
 file(STRINGS test.utf8 infile_strings ENCODING UTF-8)
 list(LENGTH infile_strings content_len)

Tests/StringFileTest/s1-max-length.srec

@@ -0,0 +1,2 @@
+S107000001020304EE
+S1FF000041414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414141414100