ensure Cnf::FindFile doesn't return files below /dev/null

Very unlikely, but if the parent is /dev/null, the child empty and the
grandchild a value we returned /dev/null/value which doesn't exist, so
hardly a problem, but for best operability we should be consistent in
our work and return /dev/null always.

3 files changed, 22 insertions, 9 deletions

diff --git a/apt-pkg/contrib/configuration.cc b/apt-pkg/contrib/configuration.cc
index 3cb7fde06..9007bf9ec 100644
--- a/apt-pkg/contrib/configuration.cc
+++ b/apt-pkg/contrib/configuration.cc
@@ -225,15 +225,7 @@ string Configuration::FindFile(const char *Name,const char *Default) const
       }
       result.append(val);
    }
-
-   // do some normalisation by removing // and /./ from the path
-   size_t found = string::npos;
-   while ((found = result.find("/./")) != string::npos)
-      result.replace(found, 3, "/");
-   while ((found = result.find("//")) != string::npos)
-      result.replace(found, 2, "/");
-
-   return result;
+   return flNormalize(result);
 }
 									/*}}}*/
 // Configuration::FindDir - Find a directory name			/*{{{*/
diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index e410f52d6..fa0930dff 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -694,6 +694,25 @@ string flAbsPath(string File)
    return AbsPath;
 }
 									/*}}}*/
+std::string flNormalize(std::string file)				/*{{{*/
+{
+   if (file.empty())
+      return file;
+   // do some normalisation by removing // and /./ from the path
+   size_t found = string::npos;
+   while ((found = file.find("/./")) != string::npos)
+      file.replace(found, 3, "/");
+   while ((found = file.find("//")) != string::npos)
+      file.replace(found, 2, "/");
+
+   if (APT::String::Startswith(file, "/dev/null"))
+   {
+      file.erase(strlen("/dev/null"));
+      return file;
+   }
+   return file;
+}
+									/*}}}*/
 // SetCloseExec - Set the close on exec flag				/*{{{*/
 // ---------------------------------------------------------------------
 /* */
diff --git a/apt-pkg/contrib/fileutl.h b/apt-pkg/contrib/fileutl.h
index f33f7804b..c13613171 100644
--- a/apt-pkg/contrib/fileutl.h
+++ b/apt-pkg/contrib/fileutl.h
@@ -234,6 +234,8 @@ std::string flCombine(std::string Dir,std::string File);
 /** \brief Takes a file path and returns the absolute path
  */
 std::string flAbsPath(std::string File);
+/** \brief removes superfluous /./ and // from path */
+APT_HIDDEN std::string flNormalize(std::string file);
 
 // simple c++ glob
 std::vector<std::string> Glob(std::string const &pattern, int flags=0);