Add initial su(1)

Makefile

@@ -36,6 +36,7 @@ SRC = \
 	pivot_root.c        \
 	ps.c                \
 	rmmod.c             \
+	su.c                \
 	swapoff.c           \
 	swapon.c            \
 	truncate.c          \

config.mk

@@ -10,10 +10,10 @@ MANPREFIX = $(PREFIX)/share/man
 LD = $(CC)
 CPPFLAGS = -D_BSD_SOURCE -D_GNU_SOURCE
 CFLAGS   = -g -ansi -Wall -Wno-long-long $(CPPFLAGS)
-LDFLAGS  = -g
+LDFLAGS  = -g -lcrypt
 
 #CC = tcc
 #LD = $(CC)
 #CPPFLAGS = -D_BSD_SOURCE -D_GNU_SOURCE
 #CFLAGS   = -Os -Wall $(CPPFLAGS)
-#LDFLAGS  =
+#LDFLAGS  = -lcrypt

su.c

@@ -0,0 +1,94 @@
+/* See LICENSE file for copyright and license details. */
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <pwd.h>
+#include <grp.h>
+#include <shadow.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [username]\n", argv0);
+}
+
+int
+main(int argc, char **argv)
+{
+	char *usr, *pass, *cryptpass;
+	char **newargv;
+	struct spwd *spw;
+	struct passwd *pw;
+	uid_t uid;
+	int i;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc < 1)
+		usr = "root";
+	else if (argc == 1)
+		usr = argv[0];
+	else
+		usage();
+
+	uid = getuid();
+
+	spw = getspnam(usr);
+	if (!spw)
+		eprintf("getspnam: %s:", usr);
+
+	switch (spw->sp_pwdp[0]) {
+	case '!':
+	case '*':
+		enprintf(EXIT_FAILURE, "Denied\n");
+	case '$':
+		break;
+	default:
+		enprintf(EXIT_FAILURE, "Invalid shadow record\n");
+	}
+
+	if (uid) {
+		pass = getpass("Password: ");
+		if (!pass)
+			eprintf("getpass:");
+	}
+
+	cryptpass = crypt(pass, spw->sp_pwdp);
+	for (i = 0; pass[i]; i++)
+		pass[i] = '\0';
+	if (!cryptpass)
+		eprintf("crypt:");
+
+	if (strcmp(cryptpass, spw->sp_pwdp) != 0)
+		enprintf(EXIT_FAILURE, "Denied\n");
+
+	errno = 0;
+	pw = getpwnam(usr);
+	if (errno)
+		eprintf("getpwnam: %s", usr);
+	else if (!pw)
+		enprintf(EXIT_FAILURE, "getpwnam: %s: no such user\n", usr);
+
+	if (initgroups(usr, pw->pw_gid) < 0)
+		eprintf("initgroups:");
+	if (setgid(pw->pw_gid) < 0)
+		eprintf("setgid:");
+	if (setuid(pw->pw_uid) < 0)
+		eprintf("setuid:");
+
+	newargv = malloc(2 * sizeof(char *));
+	if (!newargv)
+		eprintf("malloc:");
+	newargv[0] = pw->pw_shell;
+	newargv[1] = NULL;
+	setenv("HOME", pw->pw_dir, 1);
+	execve(pw->pw_shell, newargv, environ);
+	return (errno == ENOENT) ? 127 : 126;
+}