Add initial implementation of login(1)

No shadow support atm.

Makefile

@@ -32,6 +32,7 @@ SRC = \
 	id.c                \
 	insmod.c            \
 	killall5.c          \
+	login.c             \
 	lsmod.c             \
 	lsusb.c             \
 	mknod.c             \

login.c

@@ -0,0 +1,109 @@
+/* See LICENSE file for copyright and license details. */
+#define _XOPEN_SOURCE
+#include <errno.h>
+#include <grp.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include "config.h"
+#include "util.h"
+
+static int dologin(struct passwd *, int);
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-p] username\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	struct passwd *pw;
+	uid_t uid;
+	gid_t gid;
+	char *pass, *cryptpass;
+	int pflag = 0;
+
+	ARGBEGIN {
+	case 'p':
+		pflag = 1;
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc < 1)
+		usage();
+
+	errno = 0;
+	pw = getpwnam(argv[0]);
+	if (errno)
+		eprintf("getpwnam: %s:", argv[0]);
+	else if (!pw)
+		eprintf("who are you?\n");
+
+	switch (pw->pw_passwd[0]) {
+	case '!':
+	case '*':
+		eprintf("Denied\n");
+	}
+
+	if (pw->pw_passwd[0] == 'x' && pw->pw_passwd[1] == '\0')
+		eprintf("no shadow support\n");
+
+	uid = pw->pw_uid;
+	gid = pw->pw_gid;
+
+	/* Empty password? Login now */
+	if (pw->pw_passwd[0] == '\0')
+		goto login;
+
+	/* Flush pending input */
+        ioctl(STDIN_FILENO, TCFLSH, (void *)0);
+
+	pass = getpass("Password: ");
+	if (!pass)
+		eprintf("getpass:");
+	putchar('\n');
+	cryptpass = crypt(pass, pw->pw_passwd);
+	explicit_bzero(pass, strlen(pass));
+	if (!cryptpass)
+		eprintf("crypt:");
+	if (strcmp(cryptpass, pw->pw_passwd) != 0)
+		eprintf("oops\n");
+
+login:
+	if (initgroups(argv[0], gid) < 0)
+		eprintf("initgroups:");
+	if (setgid(gid) < 0)
+		eprintf("setgid:");
+	if (setuid(uid) < 0)
+		eprintf("setuid:");
+
+	return dologin(pw, pflag);
+}
+
+static int
+dologin(struct passwd *pw, int preserve)
+{
+	char *shell[] = { pw->pw_shell, pw->pw_shell, "-l", NULL };
+
+	if (preserve == 0)
+		clearenv();
+	setenv("HOME", pw->pw_dir, 1);
+	setenv("SHELL", pw->pw_shell, 1);
+	setenv("USER", pw->pw_name, 1);
+	setenv("LOGNAME", pw->pw_name, 1);
+	setenv("PATH", strcmp(pw->pw_name, "root") == 0 ?
+	       ENV_SUPATH : ENV_PATH, 1);
+	if (chdir(pw->pw_dir) < 0)
+		eprintf("chdir %s:", pw->pw_dir);
+	execvp(shell[0], shell + 1);
+	weprintf("execvp %s:", shell[0]);
+	return (errno == ENOENT) ? 127 : 126;
+}