env flag

implemented -e flag:
it copies the elements of env that we want to keep, clears the environment and
sets it to only the saved and default elements.

also removed the code for copying the environment and allocating a new one

us.c

@@ -36,11 +36,14 @@ static int perm_set (struct passwd *, struct group *);
 static int authenticate (const char *);
 static struct passwd* user_to_passwd (const char *);
 static struct group* group_to_grp (const char *);
+//static int execvpe(const char *, char *const *, char *const *);
 
 // 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};
 
+extern char **environ;
+
 int main (int argc, char *argv[])
 {
 	// TODO: Add arguments
@@ -48,9 +51,9 @@ int main (int argc, char *argv[])
 	char *t_usr = "root", *t_grp = NULL;
 	struct passwd *t_pw;
 	struct group *t_gr;
-	int opt;
-	int shellflag = 0;
-	while ((opt = getopt(argc, argv, "A:u:g:C:s")) != -1) {
+	int opt, err;
+	int shellflag = 0, envflag = 0;
+	while ((opt = getopt(argc, argv, "A:u:g:C:se")) != -1) {
 		switch (opt) {
 		case 'A':
 			printf("-A is not yet implemented\n");
@@ -69,6 +72,9 @@ int main (int argc, char *argv[])
 		case 's':
 			shellflag = 1;
 			break;
+		case 'e':
+			envflag = 1;
+			break;
 		case '?':
 			usage();
 			exit(EINVAL);
@@ -134,10 +140,53 @@ int main (int argc, char *argv[])
 	c_argv[c_argc] = NULL;
 
 	/* Authenticate */
+	// FIXME: move this up
 	if (authenticate(uname) != PAM_SUCCESS)
 		exit(EXIT_FAILURE);
 
-	// TODO: clean up env
+	struct env_elem {
+		char *name;
+		char *value;
+	};
+
+	struct env_elem env_keep[] = {
+		{"PATH", NULL},
+		{"TERM", NULL},
+		{"EDITOR", NULL},
+		{"VISUAL", NULL},
+		{"DISPLAY", NULL},
+		{"XAUTHORITY", NULL},
+		{NULL, NULL}
+	};
+
+	struct env_elem env_mod[] = {
+		{"USER", t_pw->pw_name},
+		{"LOGNAME", t_pw->pw_name},
+		{"SHELL", t_pw->pw_shell},
+		{"HOME", t_pw->pw_dir},
+		{NULL, NULL}
+	};
+
+	if (envflag) {	/* clear env */
+		for (int i = 0; env_keep[i].name; i++)
+			env_keep[i].value = strdup(getenv(env_keep[i].name));
+		environ = NULL; // in place of clearenv
+	}
+
+	for (int i = 0; env_mod[i].name; i++) {
+		// TODO: check err value
+		err = setenv(env_mod[i].name, env_mod[i].value, 1);
+	}
+
+	if (envflag) {
+		for (int i = 0; env_keep[i].name; i++) {
+			// TODO: check err value
+			if (env_keep[i].value)
+				err = setenv(env_keep[i].name, env_keep[i].value, 1);
+		}
+	}
+	// do not override, we might be under more levels of 'us'
+	err = setenv("US_USER", my_pw->pw_name, 0);
 
 	errno = 0;
 	/* Set permissions */
@@ -147,7 +196,6 @@ int main (int argc, char *argv[])
 	}
 
 	/* Execute the command */
-	int err;
 	err = execvp(c_argv[0], c_argv);
 	if (err == -1)
 		fprintf(stderr, "execl: %s\n", strerror(errno));
@@ -171,7 +219,7 @@ static inline void usage (void)
 	// -c [file]: manually select config file
 	// something about environment
 	// something about non interactiveness
-	printf("usage: us [-s] [-u user] [-g group] command [args]\n");
+	printf("usage: us [-se] [-u user] [-g group] command [args]\n");
 }
 
 static int perm_set (struct passwd *pw, struct group *gr)
@@ -305,3 +353,42 @@ static struct group* group_to_grp (const char *group)
 	}
 	return gr;
 }
+
+/*
+static int execvpe(const char *file, char *const argv[], char *const envp[])
+{
+	const char *p, *z, *path = getenv("PATH");
+	size_t l, k;
+
+	errno = ENOENT;
+	if (!*file) return -1;
+
+	if (strchr(file, '/'))
+		return execve(file, argv, envp);
+
+	if (!path) path = "/usr/local/bin:/bin:/usr/bin";
+	k = strnlen(file, NAME_MAX+1);
+	if (k > NAME_MAX) {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	l = strnlen(path, PATH_MAX-1)+1;
+
+	for(p=path; ; p=z) {
+		char b[l+k+1];
+		z = strchr(p, ':');
+		if (!z) z = p+strlen(p);
+		if ((size_t)(z-p) >= l) {
+			if (!*z++) break;
+			continue;
+		}
+		memcpy(b, p, z-p);
+		b[z-p] = '/';
+		memcpy(b+(z-p)+(z>p), file, k+1);
+		execve(b, argv, envp);
+		if (errno != ENOENT) return -1;
+		if (!*z++) break;
+	}
+	return -1;
+}
+*/