pty: use /bin/login by default

kmscon does always pass a proper argv array so the default is never used.
However, for security reasons we shouldn't hardcode /bin/login. If some
other program uses the pty layer and forgets to pass in a suitable argv
all the time, they mind end up with opening a root shell.

Hence, use /bin/login as default.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>

src/pty.c

@@ -201,7 +201,7 @@ exec_child(const char *term, char **argv, const char *seat)
 	if (!term)
 		term = "vt220";
 	if (!argv)
-		argv = (char*[]){ "/bin/sh", "-l", NULL };
+		argv = (char*[]){ "/bin/login", NULL };
 
 	setenv("TERM", term, 1);
 	if (seat)