khan/main.c

#include <sys/stat.h>

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

#define BUFF_LEN_1	 1000
#define BUFF_LEN_2	 1025
#define BUFF_LEN_3	 1024
#define DEFAULT_CHROOT	 "/var/gopher/"


void 		display_file(const char *);
void 		drop_privileges(const char *, const char *);

void
drop_privileges(const char *user, const char *path)
{
	struct passwd  *pw;
	char 		chroot_dir[BUFF_LEN_2];

	strlcpy(chroot_dir, path, sizeof(chroot_dir));

	/*
	 * use chroot() if an user is specified requires root user to be
	 * running the program to run chroot() and then drop privileges
	 */
	if (strlen(user) > 0) {

		/* is root? */
		if (getuid() != 0) {
			syslog(LOG_DAEMON, "chroot requires program to be run as root");
			errx(1, "chroot requires root user");
		}
		/* search user uid from name */
		if ((pw = getpwnam(user)) == NULL) {
			syslog(LOG_DAEMON, "the user %s can't be found on the system", user);
			err(1, "finding user");
		}
		/* chroot worked? */
		if (chroot(chroot_dir) != 0) {
			syslog(LOG_DAEMON, "the chroot_dir %s can't be used for chroot", chroot_dir);
			err(1, "chroot");
		}
		if (chdir("/") == -1) {
			syslog(LOG_DAEMON, "failed to chdir(\"/\")");
			err(1, "chdir");
		}
		/* drop privileges */
		if (setgroups(1, &pw->pw_gid) ||
		    setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
		    setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid)) {
			syslog(LOG_DAEMON, "dropping privileges to user %s (uid=%i) failed",
			       user, pw->pw_uid);
			err(1, "Can't drop privileges");
		}
		strlcpy(chroot_dir, "/", sizeof(chroot_dir));
	}
#ifdef __OpenBSD__
	/*
    	 * prevent access to files other than the one in path
    	 */
	if (unveil(chroot_dir, "r") == -1) {
		syslog(LOG_DAEMON, "unveil on %s failed", chroot_dir);
		err(1, "unveil");
	}
	/*
	 * prevent system calls other parsing queryfor fread file and
	 * write to stdio
	 */
	if (pledge("stdio rpath", NULL) == -1) {
		syslog(LOG_DAEMON, "pledge call failed");
		err(1, "pledge");
	}
#endif



}

void
display_file(const char *path)
{
	size_t 		buflen = BUFF_LEN_1;
	char           *buffer[BUFF_LEN_1];
	ssize_t 	nread;
	struct stat 	sb;
	FILE           *fd;

	/* this is to check if path is a directory */
	if (stat(path, &sb) == -1)
    		goto err;

	/* open the file requested */
	if ((fd = fopen(path, "r")) == NULL)
    		goto err;

	/* check if directory */
	if (S_ISDIR(sb.st_mode) == 1)
    		goto err;

	/* read the file and write it to stdout */
	while ((nread = fread(buffer, sizeof(char), buflen, fd)) != 0)
		fwrite(buffer, sizeof(char), nread, stdout);
	fclose(fd);
	syslog(LOG_DAEMON, "path served %s", path);

	return;

err:
	/* return an error code and no content */
	printf("resource not found for %s\n", path);
	syslog(LOG_DAEMON, "path invalid %s", path);
}

int
main(int argc, char **argv)
{
	char 		buffer   [BUFF_LEN_2];
	char 		request  [BUFF_LEN_2];
	char 		path     [BUFF_LEN_2] = DEFAULT_CHROOT;
	char 		user     [_SC_LOGIN_NAME_MAX] = "";
	int 		option;
	int		chroot = 0;
	char           *pos;

	while ((option = getopt(argc, argv, ":d:u:")) != -1) {
		switch (option) {
		case 'd':
			strlcpy(path, optarg, sizeof(path));
			break;
		case 'u':
			chroot = 1;
			strlcpy(user, optarg, sizeof(user));
			break;
		}
	}

	/*
	 * do chroot if an user is supplied run pledge/unveil if OpenBSD
	 */
	drop_privileges(user, path);
	if (chroot == 1)
    		strlcpy(path, "/", sizeof(path));

	/*
	 * read 1024 chars from stdin
	 * to get the request
	 */
	fgets(request, BUFF_LEN_3, stdin);

	/* remove \r\n at the end of string
         * replace \n first and then \r
         * because some client may only use
         * \n instead of \r\n
         */
	pos = strchr(request, '\n');
	if (pos != NULL) *pos = '\n';

	pos = strchr(request, '\r');
	if (pos != NULL) *pos = '\0';

	syslog(LOG_DAEMON, "request %s", request);

	/*
	 * look for the first / after the hostname
	 * in order to split hostname and uri
	 */
	 fprintf(stderr, "<%s %ld>\n", request, strlen(request));
    	 if(strlen(request) == 0 || strcmp(request, "/") == 0) {
        	 fprintf(stderr, "<%s %ld>\n", request, strlen(request));
		strlcpy(request, "/gophermap", sizeof(request));
	 }

	/* add the base dir to the file requested */
	strlcat(path, request, sizeof(path));

	/* open file and send it to stdout */
	display_file(path);

	return (0);
}