Allow running of arbitrary commands before and after authentication

README.md

@@ -58,6 +58,9 @@ The following command-line arguments are supported:
     -l       only lock console switching
     -L       only enable console switching
     -m       mute kernel messages on console while physlock is running
+    -b CMD   execute CMD before the password prompt
+    -a CMD   execute CMD after successfully authenticating
+    -n       don't actually authenticate: just execute commands
     -p MSG   Display MSG before the password prompt
     -s       disable sysrq key while physlock is running
     -v       print version information and exit

main.c

@@ -26,13 +26,15 @@
 #include <errno.h>
 #include <pwd.h>
 #include <signal.h>
+#include <sys/wait.h>
 #include <security/pam_misc.h>
 
 static int oldvt;
 static vt_t vt;
 static int oldsysrq;
 static int oldprintk;
 static pid_t chpid;
+static int cmdpid;
 static int locked;
 static userinfo_t root, user;
 
@@ -67,8 +69,8 @@ CLEANUP void free_user(userinfo_t *uinfo) {
 }
 
 void cleanup() {
-	if (options->detach && chpid > 0)
-		/* No cleanup in parent after successful fork */
+	if ((options->detach && chpid > 0) || cmdpid == 0)
+		/* No cleanup in parent after successful fork or in failed forked command */
 		return;
 	free_user(&user);
 	free_user(&root);
@@ -98,17 +100,46 @@ void setup_signal(int signum, void (*handler)(int)) {
 	sigact.sa_flags = 0;
 	sigact.sa_handler = handler;
 	sigemptyset(&sigact.sa_mask);
-	
+
 	if (sigaction(signum, &sigact, NULL) < 0)
 		error(0, errno, "signal %d", signum);
 }
 
+void drop_privileges(userinfo_t* user) {
+	struct passwd *p = getpwnam(user->name);
+	if (p == NULL) {
+		error(EXIT_FAILURE, errno, "get user passwd data");
+	}
+
+	if (setgid(p->pw_gid) != 0) {
+		error(EXIT_FAILURE, errno, "setgid");
+	}
+
+	if (setuid(p->pw_uid) != 0) {
+		error(EXIT_FAILURE, errno, "setuid");
+	}
+}
+
+void run_command(const char* cmd, userinfo_t* user) {
+	cmdpid = fork();
+	if (cmdpid < 0) {
+		error(EXIT_FAILURE, errno, "fork");
+	} else if (cmdpid > 0) {
+		wait(NULL);
+	} else {
+		drop_privileges(user);
+		execl("/bin/sh", "sh", "-c", cmd, NULL);
+		error(EXIT_FAILURE, errno, "exec");
+	}
+}
+
 int main(int argc, char **argv) {
 	int try = 0, root_user = 1;
 	uid_t owner;
 	userinfo_t *u = &user;
 
 	oldvt = oldsysrq = oldprintk = vt.nr = vt.fd = -1;
+	cmdpid = -1;
 	vt.ios = NULL;
 
 	error_init(2);
@@ -180,11 +211,15 @@ int main(int argc, char **argv) {
 	dup2(vt.fd, 1);
 	dup2(vt.fd, 2);
 
+	if (options->command_before != NULL && options->command_before[0] != '\0') {
+		run_command(options->command_before, &user);
+	}
+
 	if (options->prompt != NULL && options->prompt[0] != '\0') {
 		fprintf(vt.ios, "%s\n\n", options->prompt);
 	}
 
-	locked = 1;
+	locked = !options->no_auth;
 
 	while (locked) {
 		if (!root_user && try >= (u == &root ? 1 : 3)) {
@@ -218,6 +253,10 @@ int main(int argc, char **argv) {
 		}
 	}
 
+	if (options->command_after != NULL && options->command_after[0] != '\0') {
+		run_command(options->command_after, &user);
+	}
+
 	return 0;
 }
 

options.c

@@ -28,7 +28,7 @@ static options_t _options;
 const options_t *options = (const options_t*) &_options;
 
 void print_usage() {
-	printf("usage: physlock [-dhLlmsv] [-p MSG]\n");
+	printf("usage: physlock [-dhLlmsbanv] [-p MSG]\n");
 }
 
 void print_version() {
@@ -37,16 +37,17 @@ void print_version() {
 
 void parse_options(int argc, char **argv) {
 	int opt;
-	
+
 	progname = strrchr(argv[0], '/');
 	progname = progname != NULL ? progname + 1 : argv[0];
 
 	_options.detach = 0;
 	_options.disable_sysrq = 0;
 	_options.lock_switch = -1;
 	_options.mute_kernel_messages = 0;
+	_options.no_auth = 0;
 
-	while ((opt = getopt(argc, argv, "dhLlmp:sv")) != -1) {
+	while ((opt = getopt(argc, argv, "dhLlmnp:svb:a:")) != -1) {
 		switch (opt) {
 			case '?':
 				print_usage();
@@ -66,9 +67,18 @@ void parse_options(int argc, char **argv) {
 			case 'm':
 				_options.mute_kernel_messages = 1;
 				break;
+			case 'n':
+				_options.no_auth = 1;
+				break;
 			case 'p':
 				_options.prompt = optarg;
 				break;
+			case 'b':
+				_options.command_before = optarg;
+				break;
+			case 'a':
+				_options.command_after = optarg;
+				break;
 			case 's':
 				_options.disable_sysrq = 1;
 				break;

physlock.1

@@ -3,9 +3,13 @@
 physlock \- lock all consoles / virtual terminals
 .SH SYNOPSIS
 .B physlock
-.RB [ \-dhLlmsv ]
+.RB [ \-dhLlmnsv ]
 .RB [ \-p
 .IR MSG ]
+.RB [ \-b
+.IR CMD ]
+.RB [ \-a
+.IR CMD ]
 .SH DESCRIPTION
 physlock is an alternative to vlock, it is equivalent to `vlock \-an'. It is
 written because vlock blocks some linux kernel mechanisms like hibernate and
@@ -39,6 +43,15 @@ locked.
 .B \-m
 Mute kernel messages on console while physlock is running.
 .TP
+.B "\-b " CMD
+Execute CMD before asking for password
+.TP
+.B "\-a " CMD
+Execute CMD after asking for password
+.TP
+.B \-n
+Don't ask for authentication: just execute commands
+.TP
 .BI "\-p " MSG
 Display
 .I MSG

physlock.h

@@ -54,7 +54,10 @@ typedef struct options_s {
 	int disable_sysrq;
 	int lock_switch;
 	int mute_kernel_messages;
+	int no_auth;
 	const char *prompt;
+	const char *command_before;
+	const char *command_after;
 } options_t;
 
 extern const options_t *options;