Implement utmp audit (#133)

Implements utmp audit required by policykit.

This commit also flattens the pidtree for the DM by starting the
display environment directly in the first fork which already should
have the environment ready for this purpose. This is with the
exception of xorg environments where this can't be done that easily.

src/login.c

@@ -18,6 +18,7 @@
 #include <sys/stat.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <utmp.h>
 #include <xcb/xcb.h>
 
 int get_free_display()
@@ -271,6 +272,38 @@ void env_xdg(const char* tty_id, const enum display_server display_server)
 	}
 }
 
+void add_utmp_entry(
+	struct utmp *entry,
+	char *username,
+	pid_t display_pid
+) {
+	entry->ut_type = USER_PROCESS;
+	entry->ut_pid = display_pid;
+	strcpy(entry->ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
+
+	/* only correct for ptys named /dev/tty[pqr][0-9a-z] */
+	strcpy(entry->ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
+
+	time((long int *) &entry->ut_time);
+
+	strncpy(entry->ut_user, username, UT_NAMESIZE);
+	memset(entry->ut_host, 0, UT_HOSTSIZE);
+	entry->ut_addr = 0;
+	setutent();
+
+	pututline(entry);
+}
+
+void remove_utmp_entry(struct utmp *entry) {
+	entry->ut_type = DEAD_PROCESS;
+	memset(entry->ut_line, 0, UT_LINESIZE);
+	entry->ut_time = 0;
+	memset(entry->ut_user, 0, UT_NAMESIZE);
+	setutent();
+	pututline(entry);
+	endutent();
+}
+
 void xauth(const char* display_name, const char* shell, const char* home)
 {
 	char xauthority[256];
@@ -310,8 +343,6 @@ void xorg(
 	const char* vt,
 	const char* desktop_cmd)
 {
-	reset_terminal(pwd);
-
 	// generate xauthority file
 	xauth(display_name, pwd->pw_shell, pwd->pw_dir);
 
@@ -365,7 +396,6 @@ void xorg(
 
 	int status;
 	waitpid(xorg_pid, &status, 0);
-	reset_terminal(pwd);
 	xcb_disconnect(xcb);
 	kill(pid, 0);
 
@@ -380,50 +410,29 @@ void wayland(
 	struct passwd* pwd,
 	const char* desktop_cmd)
 {
-	reset_terminal(pwd);
-	pid_t pid = fork();
-	
-	if (pid == 0)
-	{
-		char cmd[1024];
-		snprintf(cmd, 1024, "%s %s", config.wayland_cmd, desktop_cmd);
-		execl(pwd->pw_shell, pwd->pw_shell, "-c", cmd, NULL);
-		exit(EXIT_SUCCESS);
-	}
 
-	int status;
-	waitpid(pid, &status, 0);
-	reset_terminal(pwd);
+	char cmd[1024];
+	snprintf(cmd, 1024, "%s %s", config.wayland_cmd, desktop_cmd);
+	execl(pwd->pw_shell, pwd->pw_shell, "-c", cmd, NULL);
 }
 
 void shell(struct passwd* pwd)
 {
-	reset_terminal(pwd);
-	pid_t pid = fork();
+	const char* pos = strrchr(pwd->pw_shell, '/');
+	char args[1024];
+	args[0] = '-';
 
-	if (pid == 0)
+	if (pos != NULL)
 	{
-		const char* pos = strrchr(pwd->pw_shell, '/');
-		char args[1024];
-		args[0] = '-';
-
-		if (pos != NULL)
-		{
-			pos = pos + 1;
-		}
-		else
-		{
-			pos = pwd->pw_shell;
-		}
-
-		strncpy(args + 1, pos, 1024);
-		execl(pwd->pw_shell, args, NULL);
-		exit(EXIT_SUCCESS);
+		pos = pos + 1;
+	}
+	else
+	{
+		pos = pwd->pw_shell;
 	}
 
-	int status;
-	waitpid(pid, &status, 0);
-	reset_terminal(pwd);
+	strncpy(args + 1, pos, 1024);
+	execl(pwd->pw_shell, args, NULL);
 }
 
 // pam_do performs the pam action specified in pam_action
@@ -597,6 +606,7 @@ void auth(
 			exit(EXIT_FAILURE);
 		}
 
+		reset_terminal(pwd);
 		switch (desktop->display_server[desktop->cur])
 		{
 			case DS_WAYLAND:
@@ -620,9 +630,16 @@ void auth(
 		exit(EXIT_SUCCESS);
 	}
 
+	// add utmp audit
+	struct utmp entry;
+	add_utmp_entry(&entry, pwd->pw_name, pid);
+
 	// wait for the session to stop
 	int status;
 	waitpid(pid, &status, 0);
+	remove_utmp_entry(&entry);
+
+	reset_terminal(pwd);
 
 	// reinit termbox
 	tb_init();