/* exec.c 1.0.4 by Pat Szuta <perly@xnet.com>
 *
 * exec.c is a kernel module which allows administrators to log all the
 * commands executed by users.  Although many have done this sort of
 * thing,  I haven't seen any public releases, so here it is.  
 * The basic output looks like this:
Nov 15 00:42:27 perly kernel: EXECVE(0)[4837]: /bin/ps uax
 * The EXECVE()[] format is: EXECVE(UID)[PID].
 * I suggest redirecting kern.info to your own file, because that's where 
 * exec.c will log its stuff. You can do this by adding this line to
 * your /etc/sysconf.log, and restarting it:
kern.info	/path/to/myfile
 * Applaud gersh for catching a nasty little syslog thingy that caused
 * the output to be printed twice. 
 * Do whatever you want with this code, just leave my name on it.  If you 
 * have any comments/questions/mods,  send them to perly@xnet.com
 * Oh, and if you do use this module, drop me an email, so that if I
 * update it, you'll be the first one to know.  Good luck :)
 * To compile and execute:
gcc exec.c -c
insmod exec.o
 * Changelog:
 dec 6, 99
  I have just recieved an email from Pavel Urban (<urbanp@mlp.cz>) with
  code to fix a major bug!! Thanks Pavel!!!!!!
  He says that the accual person who found the bug is Belgarat
  (svatopluk.dedic@netbeans.cz). Thanks a lot to him too!
 nov 18, 99
  Recieving not too many complaints,  I have decided to make this into
  a stable version.
  I have noticed that if a user does 'ls *' in a big directory,  the shell
  will expand the * to all the files in the directory and pass them as
  arguments.  Thus I have limited the number of arguments logged to 10.
  This should be enough for everyone,  and enough to keep syslog from
  bugging you about long prints :) (You can change the define if you want
  to).
 nov 18, 99
  After a bug report,  I have improved the pointer error checking routine. 
  Before it would not log any arguments, now it should.  Note that this is 
  the beta version.
 nov 15, 99
  Gersh caught a rather nasty bug.  If a user wrote a program which did
  execl("some", "stuff"); without a NULL at the end, the kernel would
  oops.  So, I added a little pointer checking.
*/

#define MODULE
#define __KERNEL__
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/unistd.h>
#include <sys/syscall.h>
#include <linux/mm.h>
#include <linux/smp_lock.h>
#include <asm/ptrace.h>
#include <errno.h>

#define ARGS_LOGGED 	10	/* Max number of arguments logged */

int (*orig_execve)(struct pt_regs);
void execve_log(char *, char **);

extern void *sys_call_table[];

int hacked_execve(struct pt_regs regs)
{
   int error;
   char * filename;

   lock_kernel();
  
   filename = getname((char *) regs.ebx);

   error = PTR_ERR(filename);

   if (IS_ERR(filename))
      goto out;

   execve_log(filename, (char **) regs.ecx);

   error = do_execve(filename, (char **) regs.ecx, (char **) regs.edx, &regs);        

   if (error == 0)
      current->flags &= ~PF_DTRACE;

   putname(filename);

out:
   unlock_kernel();
   return error;
}

void execve_log(char *file, char **argv)
{
   int args_logged = ARGS_LOGGED;
   char *tmp; 	/* pavel/belgarat's fix */

   printk(KERN_INFO "EXECVE(%d)[%d]: %s ", current->uid, current->pid,
          file);
   
   *argv++;

   while(*argv && args_logged--)
   {
      if(IS_ERR(tmp = getname(*argv))) /* Pointer checking, changed dec 6, 99 */
         break;
      printk("%s ", tmp);
      putname(tmp); /* (frees up what getname allocated) */
   }

   printk("\n");
}

int init_module(void)
{
   orig_execve = sys_call_table[SYS_execve];
   sys_call_table[SYS_execve] = hacked_execve;
   printk(KERN_INFO "execve() backdoor version 1.0.4 by Perly loaded.\n");

   return(0);
}

void cleanup_module(void)
{
   sys_call_table[SYS_execve] = orig_execve;
   printk(KERN_INFO "execve() backdoor version 1.0.4 by Perly unloaded.\n");
}