multiuser: New implementation of su.

We're still using the (now-deprecated) coreutils su, so this is
a replacement for that. It functions almost equivalently,
and supports the major arguments (-l, -c).

(Note that login/su to a non-root user is presently busted, though.
See #13583.)

src/bin/Jamfile

@@ -256,7 +256,7 @@ SubInclude HAIKU_TOP src bin bfs_tools ;
 SubInclude HAIKU_TOP src bin cddb_lookup ;
 SubInclude HAIKU_TOP src bin compress ;
 SubInclude HAIKU_TOP src bin consoled ;
-SubInclude HAIKU_TOP src bin coreutils ;
+#SubInclude HAIKU_TOP src bin coreutils ;
 SubInclude HAIKU_TOP src bin desklink ;
 SubInclude HAIKU_TOP src bin fwcontrol ;
 SubInclude HAIKU_TOP src bin hid_decode ;

src/bin/multiuser/Jamfile

@@ -11,6 +11,8 @@ StaticLibrary libmultiuser_utils.a : multiuser_utils.cpp ;
 
 BinCommand login : login.cpp : libmultiuser_utils.a ;
 
+BinCommand su : su.cpp : libmultiuser_utils.a ;
+
 BinCommand passwd : passwd.cpp : libmultiuser_utils.a ;
 
 BinCommand useradd : useradd.cpp ;
@@ -23,5 +25,6 @@ BinCommand groupdel : groupdel.cpp ;
 
 BinCommand groupmod : groupmod.cpp : [ TargetLibstdc++ ] ;
 
-# set set-uid bit on passwd
+# set set-uid bit on passwd, su
 MODE on passwd = 04755 ;
+MODE on su = 04755 ;

src/bin/multiuser/su.cpp

@@ -0,0 +1,127 @@
+/*
+ * Copyright 2017, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Axel Dörfler, axeld@pinc-software.de
+ *		Augustin Cavalier <waddlesplash>
+ */
+
+
+#include <SupportDefs.h>
+
+#include <errno.h>
+#include <pwd.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+#include <termios.h>
+#include <unistd.h>
+
+#include "multiuser_utils.h"
+
+
+extern const char* __progname;
+const char* kProgramName = __progname;
+
+const uint32 kRetries = 3;
+
+
+static void
+usage()
+{
+	fprintf(stderr, "usage: %s [-pl] [-c command] [username]\n", kProgramName);
+	exit(1);
+}
+
+
+int
+main(int argc, char *argv[])
+{
+	bool loginShell = false;
+	const char* command = NULL;
+
+	char c;
+	while ((c = getopt(argc, argv, "c:l")) != -1) {
+		switch (c) {
+			case 'l':
+				loginShell = true;
+				break;
+
+			case 'c':
+				command = optarg;
+				break;
+
+			default:
+				usage();
+				break;
+		}
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	const char* user = NULL;
+	if (argc > 0)
+		user = argv[0];
+
+	if (user == NULL)
+		user = "user";
+		// aka 'root' on Haiku
+
+	// login
+
+	openlog(kProgramName, 0, LOG_AUTH);
+
+	status_t status = B_ERROR;
+	struct passwd* passwd = NULL;
+
+	status = authenticate_user("password: ", user, &passwd, NULL,
+		kRetries, false);
+
+	if (status < B_OK || !passwd) {
+		if (passwd != NULL)
+			syslog(LOG_NOTICE, "su failed for \"%s\"", passwd->pw_name);
+		else
+			syslog(LOG_NOTICE, "su attempt for non-existent user \"%s\"", user);
+		exit(1);
+	}
+
+	// setup environment for the user
+
+	status = setup_environment(passwd, true, false);
+	if (status < B_OK) {
+		// refused login
+		fprintf(stderr, "%s: Refused login. Setting up environment failed: %s\n",
+			kProgramName, strerror(status));
+		syslog(LOG_NOTICE, "su refused for \"%s\"", passwd->pw_name);
+		exit(1);
+	}
+
+	syslog(LOG_INFO, "su as \"%s\"", passwd->pw_name);
+
+	// start shell
+	const char* args[] = {getenv("SHELL"), NULL, NULL, NULL, NULL};
+	int nextarg = 1;
+	if (loginShell) {
+		args[nextarg++] = "-login";
+	}
+	if (command != NULL) {
+		args[nextarg++] = "-c";
+		args[nextarg++] = command;
+	}
+
+	execv(args[0], (char **)args);
+
+	// try default shell
+	args[0] = "/bin/sh";
+	execv(args[0], (char **)args);
+
+	fprintf(stderr, "%s: starting the shell failed: %s", kProgramName,
+		strerror(errno));
+
+	return 1;
+}
+