implemented shell wrapper

commands are now run in a subshell, this is often needed for chains of commands
where it is not the main command to need the privilege but a subcommand does,
for example

us echo 30 > /sys/class/backlight/*/brightness

it is not echo that needs the elevated privilege but the redirection '>' does.

us.c

@@ -33,8 +33,10 @@
 
 static void usage (void);
 static int perm_set (const char *, const char *);
+static int authenticate (const char *);
 
-// FIXME: misc_conv is a separate library, should stick to plain PAM
+// FIXME: misc_conv is a separate library, should stick to plain PAM or make
+// our own pam module
 static struct pam_conv conv = {misc_conv, NULL};
 
 int main (int argc, char *argv[])
@@ -66,14 +68,16 @@ int main (int argc, char *argv[])
 		}
 	}
 
-	// Copy argv and argc
+/*
-	int c_argc = argc - optind;
+	int c_argc = argc - optind + 2;
 	char **c_argv = malloc((c_argc + 1) * sizeof(char *));
 	if (!c_argv) {
 		fprintf(stderr, "malloc: %s\n", strerror(errno));
 		goto fail_end;
 	}
-	for (int i = 0; optind < argc; i++, optind++) {
+	c_argv[0] = shell;
+	c_argv[1] = "-c";
+	for (int i = 2; optind < argc; i++, optind++) {
 		c_argv[i] = strdup(argv[optind]);
 		if (!c_argv[i]) {
 			fprintf(stderr, "getpwid: %s\n", strerror(errno));
@@ -81,45 +85,50 @@ int main (int argc, char *argv[])
 		}
 	}
 	c_argc[c_argv] = NULL;
+*/
 
-	if (c_argc == 0) {
+	/* Set argc and argv */
-		usage();
+	// TODO: get the right shell for the user (it is in the passwd struct)
-		exit(EINVAL);
+	char *shell = "/bin/sh";
+	char *command, **c_argv;
+	int size, popind = optind;
+	int c_argc = 3; // /bin/sh -c command
+
+	c_argv = malloc((c_argc + 1) * sizeof(char *));
+	if (!c_argv) {
+		fprintf(stderr, "malloc: %s\n", strerror(errno));
+		exit(errno);
 	}
 
+	for (size = 0; optind < argc; optind++)
+		size += strlen(argv[optind]) + 1;
+	command = malloc(sizeof(char) * size);
+	if (!command) {
+		fprintf(stderr, "malloc: %s\n", strerror(errno));
+		exit(errno);
+	}
+	for (optind = popind; optind < argc; optind++) {
+		strcat(command, argv[optind]);
+		strcat(command, " ");
+	}
+
+	c_argv[0] = shell;
+	// FIXME: this should be optional if size is zero: we want just a shell
+	c_argv[1] = "-c";
+	c_argv[2] = command;
+	c_argv[c_argc] = NULL;
+
+	/* Authenticate */
 	uid_t ruid = getuid();
 	struct passwd *pw = getpwuid(ruid);
 	if (!pw) {
 		fprintf(stderr, "getpwid: %s\n", strerror(errno));
-		exit(errno);
+		return errno;
 	}
 	const char *uname = pw->pw_name;
+	if (authenticate(uname) != PAM_SUCCESS)
+		exit(EXIT_FAILURE);
 
-	pam_handle_t *pamh;
-	int pam_err, count = 0;
-	pam_err = pam_start("User Switcher", uname, &conv, &pamh);
-	if (pam_err != PAM_SUCCESS) {
-		fprintf(stderr, "pam_start: %s\n", pam_strerror(pamh, pam_err));
-		exit(pam_err);
-	}
-
-	do {
-		pam_err = pam_authenticate(pamh, 0);
-		if (pam_err != PAM_SUCCESS)
-			printf("Auth failed: %s\n", pam_strerror(pamh, pam_err));
-		count++;
-	} while (pam_err != PAM_SUCCESS && count < 4);
-	if (pam_err != PAM_SUCCESS) {
-		fprintf(stderr, "better luck next time\n");
-		pam_end(pamh, pam_err);
-		exit(pam_err);
-	}
-	// FIXME: check again for the validity of the login for more security
-	// as in: https://docs.oracle.com/cd/E19120-01/open.solaris/819-2145/pam-20/index.html
-	// FIXME: ^C [SIGINT] will interrupt this call possibly causing a
-	// vulnerability
-
-	pam_end(pamh, pam_err);
 	// TODO: clean up env
 
 	errno = 0;
@@ -130,7 +139,7 @@ int main (int argc, char *argv[])
 	}
 
 	/* Execute the command */
-	if (execvp(*c_argv, c_argv) == -1) // execvp searches in path
+	if (execv(*c_argv, c_argv) == -1) // execvp searches in path
 		fprintf(stderr, "execv: %s\n", strerror(errno));
 
 	/* Cleanup and return */
@@ -231,3 +240,35 @@ static int perm_set (const char	*user, const char *group)
 
 	return 0;
 }
+
+static int authenticate (const char *uname)
+{
+	pam_handle_t *pamh;
+	int pam_err, count = 0;
+	pam_err = pam_start("User Switcher", uname, &conv, &pamh);
+	if (pam_err != PAM_SUCCESS) {
+		fprintf(stderr, "pam_start: %s\n", pam_strerror(pamh, pam_err));
+		return pam_err;
+	}
+
+	do {
+		pam_err = pam_authenticate(pamh, 0);
+		if (pam_err != PAM_SUCCESS)
+			printf("Auth failed: %s\n", pam_strerror(pamh, pam_err));
+		// FIXME: count gets ignored because authentication service has
+		// a set amount of retries giving an error:
+		// Have exhausted maximum number of retries for service
+		count++;
+	} while (pam_err != PAM_SUCCESS && count < 4);
+	if (pam_err != PAM_SUCCESS) {
+		fprintf(stderr, "better luck next time\n");
+		pam_end(pamh, pam_err);
+		return pam_err;
+	}
+	// FIXME: check again for the validity of the login for more security
+	// as in: https://docs.oracle.com/cd/E19120-01/open.solaris/819-2145/pam-20/index.html
+	// FIXME: ^C [SIGINT] will interrupt this call possibly causing a
+	// vulnerability
+
+	return pam_end(pamh, pam_err);
+}