gemini server written in C used with inetd
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#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <ctype.h>
#include <dirent.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pwd.h>
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#include <stdarg.h>
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#include <stdio.h>
#include <stdlib.h>
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#include <string.h>
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#include <syslog.h>
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#include <unistd.h>
#include "mimes.h"
#include "opts.h"
#include "utils.h"
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/* lenght of "gemini://" */
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#define GEMINI_PART 9
/*
* number of bytes to read with fgets() : 2014 + 1
* fgets() reads at most size-1 (1024 here)
* see https://gemini.circumlunar.space/docs/specification.html.
*/
#define GEMINI_REQUEST_MAX 1025
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void autoindex(const char *);
void cgi(const char *cgicmd);
void display_file(const char *);
void drop_privileges(const char *, const char *);
void echdir(const char *);
void status(const int, const char *);
void status_redirect(const int, const char *);
void status_error(const int, const char*);
int uridecode(char *);
void
echdir(const char *path)
{
if (chdir(path) == -1) {
switch (errno) {
case ENOTDIR: /* FALLTHROUGH */
case ENOENT:
status_error(51, "file not found");
break;
case EACCES:
status_error(50, "Forbidden path");
break;
default:
status_error(50, "Internal server error");
break;
}
errlog("failed to chdir(%s)", path);
}
}
int
uridecode(char *uri)
{
int n = 0;
char c = '\0';
long l = 0;
char *pos = NULL;
if ((pos = strchr(uri, '%')) == NULL) {
return n;
}
while ((pos = strchr(pos, '%')) != NULL) {
if (strlen(pos) < 3) {
return n;
}
char hex[3] = {'\0'};
for (size_t i=0; i < 2; i++) {
hex[i] = tolower(pos[i+1]);
}
errno = 0;
l = strtol(hex, 0, 16);
if (errno == ERANGE && (l == LONG_MAX || l == LONG_MIN)) {
/* conversion failed */
continue;
}
c = (char)l;
pos[0] = c;
/* rewind of two char to remove %hex */
memmove(pos+1 , pos + 3, strlen(pos+3) + 1); /* +1 for \0*/
n++;
pos++; /* avoid infinite loop */
}
return n;
}
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void
drop_privileges(const char *user, const char *path)
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{
struct passwd *pw;
/*
* 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) {
errlog("chroot requires program to be run as root");
}
/* search user uid from name */
if ((pw = getpwnam(user)) == NULL) {
errlog("the user %s can't be found on the system", user);
}
/* chroot worked? */
if (chroot(path) != 0) {
errlog("the chroot_dir %s can't be used for chroot", path);
}
chrooted = 1;
echdir("/");
/* drop privileges */
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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)) {
errlog("dropping privileges to user %s (uid=%i) failed",
user, pw->pw_uid);
}
}
#ifdef __OpenBSD__
/*
* prevent access to files other than the one in path
*/
if (chrooted) {
eunveil("/", "r");
} else {
eunveil(path, "r");
}
/* permission to execute what's inside cgidir */
if (strlen(cgidir) > 0) {
eunveil(cgidir, "rx");
}
eunveil(NULL,NULL); /* no more call to unveil() */
/* promise permissions */
if (strlen(cgidir) > 0) {
epledge("stdio rpath exec", NULL);
} else {
epledge("stdio rpath", NULL);
}
#endif
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}
void
status(const int code, const char *file_mime)
{
if (strcmp(file_mime, "text/gemini") == 0) {
printf("%i %s; %s\r\n", code, file_mime, lang);
} else {
printf("%i %s\r\n", code, file_mime);
}
}
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void
status_redirect(const int code, const char *url)
{
printf("%i %s\r\n",
code, url);
}
void
status_error(const int code, const char *reason)
{
printf("%i %s\r\n",
code, reason);
}
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void
display_file(const char *fname)
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{
FILE *fd = NULL;
struct stat sb = {0};
ssize_t nread = 0;
const char *file_mime;
char *buffer[BUFSIZ];
char target[FILENAME_MAX] = {'\0'};
char tmp[PATH_MAX] = {'\0'}; /* used to build temporary path */
/* special case : fname empty. The user requested just the directory name */
if (strlen(fname) == 0) {
if (stat("index.gmi", &sb) == 0) {
/* there is index.gmi in the current directory */
display_file("index.gmi");
return;
} else if (doautoidx) {
/* no index.gmi, so display autoindex if enabled */
autoindex(".");
return;
} else {
goto err;
}
}
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/* this is to check if path exists and obtain metadata later */
if (stat(fname, &sb) == -1) {
/* check if fname is a symbolic link
* if so, redirect using its target */
if (lstat(fname, &sb) != -1 && S_ISLNK(sb.st_mode) == 1)
goto redirect;
else
goto err;
}
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/* check if directory */
if (S_ISDIR(sb.st_mode) != 0) {
/* no ending "/", redirect to "fname/" */
estrlcpy(tmp, fname, sizeof(tmp));
estrlcat(tmp, "/", sizeof(tmp));
status_redirect(31, tmp);
return;
}
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/* open the file requested */
if ((fd = fopen(fname, "r")) == NULL) { goto err; }
file_mime = get_file_mime(fname, default_mime);
status(20, file_mime);
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/* read the file byte after byte in buffer and write it to stdout */
while ((nread = fread(buffer, 1, sizeof(buffer), fd)) != 0)
fwrite(buffer, 1, nread, stdout);
goto closefd; /* close file descriptor */
syslog(LOG_DAEMON, "path served %s", fname);
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return;
err:
/* return an error code and no content */
status_error(51, "file not found");
syslog(LOG_DAEMON, "path invalid %s", fname);
goto closefd;
redirect:
/* read symbolic link target to redirect */
if (readlink(fname, target, FILENAME_MAX) == -1) {
goto err;
}
status_redirect(30, target);
syslog(LOG_DAEMON, "redirection from %s to %s", fname, target);
closefd:
if (S_ISREG(sb.st_mode) != 0) {
fclose(fd);
}
}
void
autoindex(const char *path)
{
/* display liks to files in path + a link to parent (..) */
int n = 0;
struct dirent **namelist; /* this must be freed at last */
syslog(LOG_DAEMON, "autoindex: %s", path);
/* use alphasort to always have the same order on every system */
if ((n = scandir(path, &namelist, NULL, alphasort)) < 0) {
status_error(50, "Internal server error");
errlog("Can't scan %s", path);
} else {
status(20, "text/gemini");
printf("=> .. ../\n"); /* display link to parent */
for(int j = 0; j < n; j++) {
/* skip self and parent */
if ((strcmp(namelist[j]->d_name, ".") == 0) ||
(strcmp(namelist[j]->d_name, "..") == 0)) {
continue;
}
/* add "/" at the end of a directory path */
if (namelist[j]->d_type == DT_DIR) {
printf("=> ./%s/ %s/\n", namelist[j]->d_name, namelist[j]->d_name);
} else {
printf("=> ./%s %s\n", namelist[j]->d_name, namelist[j]->d_name);
}
free(namelist[j]);
}
free(namelist);
}
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}
void
cgi(const char *cgicmd)
{
/* run cgicmd replacing current process */
execl(cgicmd, cgicmd, NULL);
/* if execl is ok, this will never be reached */
status(42, "Couldn't execute CGI script");
errlog("error when trying to execl %s", cgicmd);
exit(1);
}
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int
main(int argc, char **argv)
{
char request [GEMINI_REQUEST_MAX] = {'\0'};
char user [_SC_LOGIN_NAME_MAX] = "";
char hostname [GEMINI_REQUEST_MAX] = {'\0'};
char query [PATH_MAX] = {'\0'};
char chroot_dir[PATH_MAX] = DEFAULT_CHROOT;
char file [FILENAME_MAX] = DEFAULT_INDEX;
char dir [PATH_MAX] = {'\0'};
char *pos = NULL;
int option = 0;
int virtualhost = 0;
int docgi = 0;
/*
* request : contain the whole request from client : gemini://...\r\n
* user : username, used in drop_privileges()
* hostname : extracted from hostname. used with virtualhosts and cgi SERVER_NAME
* query : file requested in cgi : gemini://...?query
* file : file basename to display. Emtpy is a directory has been requested
* dir : directory requested. vger will chdir() in to find file
* pos : used to parse request and split into interesting parts
*/
while ((option = getopt(argc, argv, ":d:l:m:u:c:vi")) != -1) {
switch (option) {
case 'd':
estrlcpy(chroot_dir, optarg, sizeof(chroot_dir));
break;
case 'l':
estrlcpy(lang, "lang=", sizeof(lang));
estrlcat(lang, optarg, sizeof(lang));
break;
case 'm':
estrlcpy(default_mime, optarg, sizeof(default_mime));
break;
case 'u':
estrlcpy(user, optarg, sizeof(user));
break;
case 'c':
estrlcpy(cgidir, optarg, sizeof(cgidir));
docgi = 1;
break;
case 'v':
virtualhost = 1;
break;
case 'i':
doautoidx = 1;
break;
}
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}
/*
* do chroot if an user is supplied
*/
drop_privileges(user, chroot_dir);
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/*
* read 1024 chars from stdin
* to get the request
* (actually 1024 + \0)
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*/
if (fgets(request, GEMINI_REQUEST_MAX, stdin) == NULL) {
/* EOF reached before reading anything */
if (feof(stdin)) {
status(59, "request is too short and probably empty");
errlog("request is too short and probably empty");
/* error before reading anything */
} else if (ferror(stdin)) {
status(59, "Error while reading request");
errlog("Error while reading request: %s", request);
}
}
/* check if string ends with '\n', or to long */
if (request[strnlen(request, GEMINI_REQUEST_MAX) - 1] != '\n') {
status(59, "request is too long (1024 max)");
errlog("request is too long (1024 max): %s", request);
}
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/* remove \r\n at the end of string */
pos = strchr(request, '\r');
if (pos != NULL)
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*pos = '\0';
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/*
* check if the beginning of the request starts with
* gemini://
*/
if (strncmp(request, "gemini://", GEMINI_PART) != 0) {
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/* error code url malformed */
errlog("request «%s» doesn't match gemini://",
request);
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}
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syslog(LOG_DAEMON, "request %s", request);
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/* remove the gemini:// part */
memmove(request, request + GEMINI_PART, strlen(request) +1 - GEMINI_PART);
/* remove all "/.." for safety reasons */
while ((pos = strstr(request, "/..")) != NULL ) {
memmove(request, pos+3, strlen(pos) +1 - 3); /* "/.." = 3 */
}
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echdir(chroot_dir); /* move to chroot */
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/* look for hostname in request : first thing before first / if any */
pos = strchr(request, '/');
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if (pos != NULL) {
/* copy what's after hostname in dir */
estrlcpy(dir, pos, strlen(pos)+1);
/* just keep hostname in request : stop the string with \0 */
pos[0] = '\0';
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}
/* check if client added :port at end of hostname and remove it */
pos = strchr(request, ':');
if (pos != NULL) {
/* end string at :*/
pos[0] = '\0';
}
/* copy hostname from request */
estrlcpy(hostname, request, sizeof(hostname));
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/* remove leading '/' in dir */
while (dir[0] == '/') {
memmove(dir, dir+1, strlen(dir+1)+1);
}
if (virtualhost) {
/* add hostname at the beginning of the dir path */
char tmp[PATH_MAX] = {'\0'};
estrlcpy(tmp, hostname, sizeof(tmp));
estrlcat(tmp, "/", sizeof(tmp));
estrlcat(tmp, dir, sizeof(tmp));
estrlcpy(dir, tmp, sizeof(dir));
}
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/* percent decode */
uridecode(dir);
/*
* split dir and filename.
* file is last part after last '/'.
* if none found, then requested file is actually a directory
*/
if (strlen(dir) > 0) {
pos = strrchr(dir, '/');
if (pos != NULL) {
estrlcpy(file, pos+1, sizeof(file)); /* +1 : no leading '/' */
pos[0] = '\0';
if (strlen(dir) > 0) {
echdir(dir); /* change directory to requested directory */
}
} else {
estrlcpy(file, dir, sizeof(file));
}
}
if (docgi) {
/* check if directory is cgidir */
char cgifp[PATH_MAX] = {'\0'};
estrlcpy(cgifp, chroot_dir, sizeof(cgifp));
if (cgifp[strlen(cgifp)-1] != '/') {
estrlcat(cgifp, "/", sizeof(cgifp));
}
estrlcat(cgifp, dir, sizeof(cgifp));
if (strcmp(cgifp, cgidir) != 0) {
/* not cgipath, display file content */
goto file_to_stdout;
}
/* set env variables for CGI */
/* see https://lists.orbitalfox.eu/archives/gemini/2020/000315.html */
esetenv("GATEWAY_INTERFACE", "CGI/1.1", 1);
esetenv("SERVER_PROTOCOL", "GEMINI", 1);
esetenv("SERVER_SOFTWARE", "vger/1", 1);
/* look for "?" if any to set query for cgi, remove it*/
pos = strchr(file, '?');
if (pos != NULL) {
estrlcpy(query, pos+1, sizeof(query));
esetenv("QUERY_STRING", query, 1);
pos[0] = '\0';
}
/* look for an extension to find PATH_INFO */
pos = strrchr(file, '.');
if (pos != NULL) {
/* found a dot */
pos = strchr(pos, '/');
if (pos != NULL) {
setenv("PATH_INFO", pos, 1);
pos[0] = '\0'; /* keep only script name */
}
}
esetenv("SCRIPT_NAME", file, 1);
esetenv("SERVER_NAME", hostname, 1);
cgi(file);
return 0;
}
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file_to_stdout:
/* regular file to stdout */
display_file(file);
return (0);
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}