settings: Avoid conf file parsing beyond allocated buffer

A valgrind analysis of libstrongswan revealed an invalid read of 1 in
the function starts_with(). A more thorough analysis proved this to be
true and showed that with a specially crafted config file (e.g. a single
'#'-character not followed by a newline), the parser might even
interpret the random memory contents following the allocated buffer as
part of the configuration file.
The way the parser is designed, it must be able to skip an inserted
'\0' and continue parsing. Since it is not able to skip two '\0'
characters, the 'fix' of allocating two more bytes than the size of the
parsed file and setting them to '\0' seems to be a safe bet.

Signed-off-by: Thomas Egerer <thomas.egerer@secunet.com>

src/libstrongswan/utils/settings.c

@@ -1244,8 +1244,8 @@ static bool parse_file(linked_list_t *contents, char *file, int level,
 	fseek(fd, 0, SEEK_END);
 	len = ftell(fd);
 	rewind(fd);
-	text = malloc(len + 1);
-	text[len] = '\0';
+	text = malloc(len + 2);
+	text[len] = text[len + 1] = '\0';
 	if (fread(text, 1, len, fd) != len)
 	{
 		free(text);