chsh should check whether shell is listed in /etc/shells for root

[CamberLoid]

Currently, chsh will check whether the shell is listed in /etc/shells for non-root users but not for root.

shadow/src/chsh.c

Lines 517 to 530 in 1f84142

	if ( !amroot
	&& ( is_restricted_shell (loginsh)
	|| (access (loginsh, X_OK) != 0))) {
	fprintf (stderr, _("%s: %s is an invalid shell\n"), Prog, loginsh);
	fail_exit (1);
	}
	/* Even for root, warn if an invalid shell is specified. */
	if (access (loginsh, F_OK) != 0) {
	fprintf (stderr, _("%s: Warning: %s does not exist\n"), Prog, loginsh);
	} else if (access (loginsh, X_OK) != 0) {
	fprintf (stderr, _("%s: Warning: %s is not executable\n"), Prog, loginsh);
	}

This may lead to a login failure when, for example, user sets shell to /bin/bash instead of /usr/bin/bash, which the former is not listed in /etc/shells. chsh should warn user that the possible invalid shell is provided.

An expected behavior is to warn the root user that Warning: $SHELL is not present in /etc/shells.

[hallyn]

Yeah I suppose that would be polite.

[hallyn]

Did you want to post a PR for this?

[jubalh]

Honestly I feel like the current settings and warnings are fine.
However I created #759 to change according to this PR.
I leave it up to the maintainers to decide which way they prefer and close this issue without merging the PR or with merging it.