/* 

lookout.c v0.1 from intrusive - (intrusive@portalofevil.com) - 

checks to see if anyone new has logged in and executes a command 
(or command string) when the specified user logs in or just 
notifies you of their presence with a beep. 

<command(s)> is either a shell-script or a quote(") encapsulated 
string containing a ';' or '&&' seperated list of commands to be 
run via a single call to system() when <username> logs in.

if "any" is given for username, notification will be delivered and
any commands specified will be executed upon the login of any user"

because utmp seems to round the login time to the minute, the login 
or logout of any user will cause the program to interpret it as
<username> logging in IF <username> is already present in utmp AND 
less than approx one minute has elapsed between the time when
<username> was recorded in the file and the time that any user has 
logged in/out.

December 8, 2002

*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <utmp.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>

main(int argc, char **argv)
{

FILE *fptr;
struct stat stbuf;
struct utmp ubuff;

time_t lastacc, logt;
int r, x = 0;
char buff[sizeof(struct utmp)];

   if((argc != 4) && (argc != 2))
   {
      fprintf(stderr, "usage: %s <username> [-e <command(s)>]\n\n", argv[0]);
      exit(1);
   }

   if(argc == 4)
   {
         if(!strncmp(argv[2], "-e", strlen(argv[2])) == 0)
         {
            fprintf(stderr, "usage: %s <username> [-e <command(s)>]\n\n", argv[0]);
            exit(1);
         }
         else
            x = 1;
   }

   if((argc > 2) && (strlen(argv[1]) > 32))
   {
      fprintf(stderr, "login names must be 32 characters or less.\n");
      exit(1);
   }

   if(stat("/var/run/utmp", &stbuf) == -1)
   {
      fprintf(stderr, "error getting file stats\n");
      exit(1);
   }

   if((r = fork()) == -1)
   {
      fprintf(stderr, "error with fork()\n");
      exit(1);
   }

   if(r > 0)
      exit(0);

lastacc = stbuf.st_mtime;

   while(1)
   {
      sleep(1);

         if(stat("/var/run/utmp", &stbuf) == -1)
         {
            fprintf(stderr, "error getting file stats\n");
            exit(1);
         }

         if(lastacc < stbuf.st_mtime)
         {
               if((fptr = fopen("/var/run/utmp", "r")) == NULL)
               {
                  fprintf(stderr, "error opening utmp\n");
                  exit(1);
               }

               while(fread(&ubuff, 1, sizeof(struct utmp), fptr))
               {
                     if((strncmp(ubuff.ut_name, argv[1], strlen(argv[1])) == 0) && (ubuff.ut_time >= lastacc))
                     {
                        printf("\a");
                        fprintf(stdout, "%s logged in\n", ubuff.ut_name);

                           if(x == 1)
                              system(argv[3]);

                        exit(0);
                     }

                     if((strncmp(argv[1], "any", 3) == 0) && (ubuff.ut_time >= lastacc))
                           if(!strstr(ubuff.ut_name, "LOGIN"))
                           {
                              printf("\a");
                              fprintf(stdout, "%s just logged in\n", ubuff.ut_name);

                                 if(x == 1)
                                    system(argv[3]);

                               exit(0);
                            }
               }
            rewind(fptr);
            lastacc = stbuf.st_mtime;            
            fclose(fptr);
         }
   }
}