Undefined behaviour in abigail::tool_utils::string_ends_with.

[Eric Fiselier <eric@efcs.ca>]

Hi Doji,

Currently string_ends_with will crash if the suffix is longer than the
string. I've attached a patch that fixes this bug.

I discovered the bug by running abicompat ./a.out <lib1> <lib2>. This
command crashed because guess_file_type will call
string_ends_with("./a.out", ".tar.gz").

/Eric

diff --git a/src/abg-tools-utils.cc b/src/abg-tools-utils.cc
index 060c6c3..f255023 100644
--- a/src/abg-tools-utils.cc
+++ b/src/abg-tools-utils.cc
@@ -324,6 +324,7 @@ check_file(const string& path,
 bool
 string_ends_with(const string& str, const string& suffix)
 {
+  if (suffix.length() > str.length()) return false;
   return str.compare(str.length() - suffix.length(),
 		     suffix.length(),
 		     suffix) == 0;