Reorder security checks for !op etc.

[ircbot] / summon.c

/*
 * usage:
 *  .../summon <real-summoner> <calling-nick> <calling-path> <channel>
 */

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

#include <utmp.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

static void check(const char *string, const char *what, int maxlen) {
  int c;
  
  if (strlen(string) > maxlen) { fprintf(stderr,"%s too long\n",what); exit(8); }
  while ((c= *string++)) {
    if (isspace((unsigned char)c) || !isprint((unsigned char)c))
      { fprintf(stderr,"bad char in %s\n",what); exit(8); }
  }
}

static void die(const char *msg) {
  fprintf(stderr,"%s\n",msg); exit(8);
}

static void problem(const char *msg) {
  printf("problem %s\n",msg);
  exit(0);
}

enum howbad { hb_notlogon, hb_noterminal, hb_nomessages, hb_ok };
static enum howbad closest= hb_notlogon;

static time_t best_idle;
static char best_line[UT_LINESIZE+1];

static void thisis(enum howbad hb) {
  if (hb > closest) closest= hb;
}

int main(int argc, const char *const *argv) {
  struct utmp *ue;
  const char *myself;
  struct stat stab;
  int fd;
  char idlebuf[20];
  
  if (argc != 5) die("bad usage");

  myself= getenv("USER");
  if (!myself) die("USER not set");
  if (strlen(myself) > UT_NAMESIZE) die("own username too long");

  check(argv[2],"nick",20);
  check(argv[3],"path",60);
  check(argv[4],"channel",20);

  if (chdir("/dev")) { perror("chdir /dev"); exit(8); }
  
  while ((errno=0, ue= getutent())) {
    if (ue->ut_type != USER_PROCESS) continue;
    if (strncmp(ue->ut_user,myself,UT_NAMESIZE)) continue;
    if (!ue->ut_line[0]) { thisis(hb_noterminal); continue; }
    ue->ut_line[UT_LINESIZE]= 0; /* overflows into next field :-/ */
    if (stat(ue->ut_line,&stab)) {
      printf("warning could not stat %s: %s\n",ue->ut_line,strerror(errno));
      thisis(hb_noterminal); continue;
    }
    if (!(stab.st_mode & S_IWGRP)) { thisis(hb_nomessages); continue; }
    closest= hb_ok;
    if (closest == hb_ok && stab.st_atime <= best_idle) continue;
    strcpy(best_line,ue->ut_line);
    best_idle= stab.st_atime;
  }
  if (errno) { perror("getutent set errno"); exit(8); }

  switch (closest) {
  case hb_notlogon:   problem("is not logged on");
  case hb_noterminal: problem("does not have any terminal/shell sessions");
  case hb_nomessages: problem("is refusing messages");
  case hb_ok: break;
  default: abort();
  }

  sprintf(idlebuf,"%lu",(unsigned long)best_idle);

  fd= open(best_line, O_NOCTTY|O_NONBLOCK|O_WRONLY);
  if (fd < 0) {
    fprintf(stderr,"unable to open terminal (%s): %s",best_line,strerror(errno));
    exit(8);
  }
  if (dup2(fd,0)) { perror("dup2"); exit(8); }
  execlp(argv[1],argv[1], best_line,idlebuf,argv[2],argv[3],argv[4], (const char*)0);
  perror(argv[1]); exit(8);
}