gemini server written in C used with inetd
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#include <sys/stat.h>
#include <err.h>
#include <errno.h>
#include <limits.h>
#include <pwd.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include "mimes.h"
#define GEMINI_PART 9
#define DEFAULT_LANG "en"
#define DEFAULT_CHROOT "/var/gemini"
#define GEMINI_REQUEST_MAX 1024 /* see https://gemini.circumlunar.space/docs/specification.html */
void display_file(const char *, const char *);
void status(const int, const char *, const char *);
void status_redirect(const int code, const char *url);
void drop_privileges(const char *, const char *);
void eunveil(const char *path, const char *permissions);
size_t estrlcat(char *dst, const char *src, size_t dstsize);
size_t estrlcpy(char *dst, const char *src, size_t dstsize);
void
eunveil(const char *path, const char *permissions)
{
if (unveil(path, permissions) == -1) {
syslog(LOG_DAEMON, "unveil on %s failed", path);
err(1, "unveil");
}
}
size_t
estrlcpy(char *dst, const char *src, size_t dstsize)
{
size_t n = 0;
n = strlcpy(dst, src, dstsize);
if (n >= dstsize) {
err(1, "estrlcpy failed");
}
return n;
}
size_t
estrlcat(char *dst, const char *src, size_t dstsize)
{
size_t size;
if ((size = strlcat(dst, src, dstsize)) >= dstsize)
err(1, "strlcat");
return size;
}
void
drop_privileges(const char *user, const char *path)
{
struct passwd *pw;
int chrooted = 0;
/*
* 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(path) != 0) {
syslog(LOG_DAEMON, "the chroot_dir %s can't be used for chroot", path);
err(1, "chroot");
}
chrooted = 1;
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");
}
}
#ifdef __OpenBSD__
/*
* prevent access to files other than the one in path
*/
if (chrooted) {
eunveil("/", "r");
} else {
eunveil(path, "r");
}
/*
* 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
status(const int code, const char *file_mime, const char *lang)
{
printf("%i %s; lang=%s\r\n",
code, file_mime, lang);
}
void
status_redirect(const int code, const char *url)
{
printf("%i %s\r\n",
code, url);
}
void
display_file(const char *path, const char *lang)
{
FILE *fd = NULL;
struct stat sb = {0};
ssize_t nread = 0;
char *buffer[BUFSIZ];
const char *file_mime;
char target[FILENAME_MAX] = "";
/* this is to check if path exists and obtain metadata later */
if (stat(path, &sb) == -1) {
/* check if path is a symbolic link
* if so, redirect using its target */
if (lstat(path, &sb) != -1 && S_ISLNK(sb.st_mode) == 1)
goto redirect;
else
goto err;
}
/* check if directory */
if (S_ISDIR(sb.st_mode) == 1)
goto err;
/* open the file requested */
if ((fd = fopen(path, "r")) == NULL)
goto err;
file_mime = get_file_mime(path);
status(20, file_mime, lang);
/* read the file and write it to stdout */
while ((nread = fread(buffer, sizeof(char), sizeof(buffer), fd)) != 0)
fwrite(buffer, sizeof(char), nread, stdout);
goto closefd;
syslog(LOG_DAEMON, "path served %s", path);
return;
err:
/* return an error code and no content */
status(51, "text/gemini", lang);
syslog(LOG_DAEMON, "path invalid %s", path);
goto closefd;
redirect:
/* read symbolic link target to redirect */
if (readlink(path, target, FILENAME_MAX) == -1) {
int errnum = errno;
fprintf(stderr, "Value of errno: %d\n", errno);
perror("Error printed by perror");
fprintf(stderr, "Error opening file: %s\n", strerror( errnum ));
goto err;
}
status_redirect(30, target);
syslog(LOG_DAEMON, "redirection from %s to %s", path, target);
closefd:
if (S_ISREG(sb.st_mode) == 1) {
fclose(fd);
}
}
int
main(int argc, char **argv)
{
char request [GEMINI_REQUEST_MAX] = {'\0'};
char hostname [GEMINI_REQUEST_MAX] = {'\0'};
char file [GEMINI_REQUEST_MAX] = {'\0'};
char path [GEMINI_REQUEST_MAX] = DEFAULT_CHROOT;
char lang [3] = DEFAULT_LANG;
char user [_SC_LOGIN_NAME_MAX] = "";
int virtualhost = 0;
int option = 0;
int chroot = 0;
char *pos = NULL;
while ((option = getopt(argc, argv, ":d:l:u:v")) != -1) {
switch (option) {
case 'd':
estrlcpy(path, optarg, sizeof(path));
break;
case 'v':
virtualhost = 1;
break;
case 'l':
estrlcpy(lang, optarg, sizeof(lang));
break;
case 'u':
estrlcpy(user, optarg, sizeof(user));
chroot = 1;
break;
}
}
/*
* do chroot if an user is supplied run pledge/unveil if OpenBSD
*/
drop_privileges(user, path);
/* change basedir to / to build the filepath if we use chroot */
if (chroot == 1)
estrlcpy(path, "/", sizeof(path));
/*
* read 1024 chars from stdin
* to get the request
*/
if (fgets(request, GEMINI_REQUEST_MAX, stdin) == NULL){
/*TODO : add error code 5x */
syslog(LOG_DAEMON, "request is too long (1024 max): %s", request);
exit(1);
}
/* remove \r\n at the end of string */
pos = strchr(request, '\r');
if (pos != NULL)
*pos = '\0';
/*
* check if the beginning of the request starts with
* gemini://
*/
if (strncmp(request, "gemini://", GEMINI_PART) != 0) {
/* error code url malformed */
syslog(LOG_DAEMON, "request «%s» doesn't match gemini://",
request);
exit(1);
}
syslog(LOG_DAEMON, "request %s", request);
/* remove the gemini:// part */
memmove(request, request + GEMINI_PART, sizeof(request) - GEMINI_PART);
/*
* look for the first / after the hostname
* in order to split hostname and uri
*/
pos = strchr(request, '/');
if (pos != NULL) {
/* if there is a / found */
/* separate hostname and uri */
estrlcpy(file, pos, strlen(pos)+1);
/* just keep hostname in request */
pos[0] = '\0';
/*
* use a default file if no file are requested this
* can happen in two cases gemini://hostname/
* gemini://hostname/directory/
*/
if (strlen(file) == 0)
estrlcpy(file, "/index.gmi", 11);
if (file[strlen(file) - 1] == '/')
estrlcat(file, "index.gmi", sizeof(file));
} else {
/*
* there are no slash / in the request
*/
estrlcpy(file, "/index.gmi", 11);
}
/* check if client added :port at end of request */
pos = strchr(request, ':');
if (pos != NULL) {
/* end string at :*/
pos[0] = '\0';
}
/* copy hostname from request */
estrlcpy(hostname, request, sizeof(hostname));
/*
* if virtualhost feature is actived looking under the default path +
* hostname directory gemini://foobar/hello will look for
* path/foobar/hello
*/
if (virtualhost) {
estrlcat(path, hostname, sizeof(path));
estrlcat(path, "/", sizeof(path));
}
/* add the base dir to the file requested */
estrlcat(path, file, sizeof(path));
/* open file and send it to stdout */
display_file(path, lang);
return (0);
}