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revise environment handling.
Add a setenv keyword for manipulating the environment. keepenv now means
only retain everything. (for one release, the old use of keepenv will still
work.)
Allow setting variables to new or existing values, and also removing vars
when keepenv is used.
ok djm martijn tb

/* $OpenBSD: env.c,v 1.3 2016/06/27 15:41:17 tedu Exp $ */
/*
 * Copyright (c) 2016 Ted Unangst <tedu@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/tree.h>

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>
#include <errno.h>

#include "doas.h"

struct envnode {
	RB_ENTRY(envnode) node;
	const char *key;
	const char *value;
};

struct env {
	RB_HEAD(envtree, envnode) root;
	u_int count;
};

static int
envcmp(struct envnode *a, struct envnode *b)
{
	return strcmp(a->key, b->key);
}
RB_GENERATE_STATIC(envtree, envnode, node, envcmp)

static struct envnode *
createnode(const char *key, const char *value)
{
	struct envnode *node;

	node = malloc(sizeof(*node));
	if (!node)
		err(1, NULL);
	node->key = strdup(key);
	node->value = strdup(value);
	if (!node->key || !node->value)
		err(1, NULL);
	return node;
}

static void
freenode(struct envnode *node)
{
	free((char *)node->key);
	free((char *)node->value);
	free(node);
}

static struct env *
createenv(struct rule *rule)
{
	struct env *env;
	u_int i;

	env = malloc(sizeof(*env));
	if (!env)
		err(1, NULL);
	RB_INIT(&env->root);
	env->count = 0;

	if (rule->options & KEEPENV) {
		extern const char **environ;

		for (i = 0; environ[i] != NULL; i++) {
			struct envnode *node;
			const char *e, *eq;
			size_t len;
			char keybuf[1024];

			e = environ[i];

			/* ignore invalid or overlong names */
			if ((eq = strchr(e, '=')) == NULL || eq == e)
				continue;
			len = eq - e;
			if (len > sizeof(keybuf) - 1)
				continue;
			memcpy(keybuf, e, len);
			keybuf[len] = '\0';

			node = createnode(keybuf, eq + 1);
			if (RB_INSERT(envtree, &env->root, node)) {
				/* ignore any later duplicates */
				freenode(node);
			} else {
				env->count++;
			}
		}
	}

	return env;
}

static char **
flattenenv(struct env *env)
{
	char **envp;
	struct envnode *node;
	u_int i;

	envp = reallocarray(NULL, env->count + 1, sizeof(char *));
	if (!envp)
		err(1, NULL);
	i = 0;
	RB_FOREACH(node, envtree, &env->root) {
		if (asprintf(&envp[i], "%s=%s", node->key, node->value) == -1)
			err(1, NULL);
		i++;
	}
	envp[i] = NULL;
	return envp;
}

static void
fillenv(struct env *env, const char **envlist)
{
	struct envnode *node, key;
	const char *e, *eq;
	const char *val;
	char name[1024];
	u_int i;
	size_t len;

	for (i = 0; envlist[i]; i++) {
		e = envlist[i];

		/* parse out env name */
		if ((eq = strchr(e, '=')) == NULL)
			len = strlen(e);
		else
			len = eq - e;
		if (len > sizeof(name) - 1)
			continue;
		memcpy(name, e, len);
		name[len] = '\0';

		/* delete previous copies */
		key.key = name;
		if (*name == '-')
			key.key = name + 1;
		if ((node = RB_FIND(envtree, &env->root, &key))) {
			RB_REMOVE(envtree, &env->root, node);
			freenode(node);
			env->count--;
		}
		if (*name == '-')
			continue;

		/* assign value or inherit from environ */
		if (eq) {
			val = eq + 1;
			if (*val == '$')
				val = getenv(val + 1);
		} else {
			val = getenv(name);
		}
		/* at last, we have something to insert */
		if (val) {
			node = createnode(name, val);
			RB_INSERT(envtree, &env->root, node);
			env->count++;
		}
	}
}

char **
prepenv(struct rule *rule)
{
	static const char *safeset[] = {
		"DISPLAY", "HOME", "LOGNAME", "MAIL",
		"PATH", "TERM", "USER", "USERNAME",
		NULL
	};
	struct env *env;
	
	env = createenv(rule);

	/* if we started with blank, fill some defaults then apply rules */
	if (!(rule->options & KEEPENV))
		fillenv(env, safeset);
	if (rule->envlist)
		fillenv(env, rule->envlist);

	return flattenenv(env);
}