/* note: this module is in beta, and has not been tested.  The author
 * makes no guarantee of it's stability or effectiveness.
 *
 *   USE AT YOUR OWN RISK!
 */

/*
 * spfx v1.0b by Justin Lesarge
 * 
 * Contact: nijenrode@india.com, irc://irc.dal.net Sorcerer
 * 
 * This module prevents security breaches (such as remote root)
 * by protecting the system from code running on the stack.  As many
 * exploits work by "smashing" the stack to execute buffered code
 * on the stack, loading this module should greatly increase system
 * security.  Examples of exploits which this module prevents are:
 * 
 * all remote root exploits for: bind/named, wu.ftpd, imap, etc..
 * 
 * this code may be freely distributed and modified, so long as credit
 * to the original author (Justin Lesarge) is left in tact.
 * 
 * to load this module, use:

     cc -c spfx.c -o ./spfx.o
     insmod ./spfx.o

 */

#define MODULE 1

#include <linux/module.h>
#include <linux/sys.h>
#include <asm/ptrace.h>

extern void *sys_call_table[];
static void *old_call_table[NR_syscalls];

#ifndef NO_DISP
# if (EBP>FS)
#  define _EBP ((EBP-2)*4)
# else
#  define _EBP (EBP*4)
# endif
# if (EIP>FS)
#  define _EIP ((EIP-2)*4)
# else
#  define _EIP (EIP*4)
# endif
# if (UESP>FS)
#  define _UESP ((UESP-2)*4)
# else
#  define _UESP (UESP*4)
# endif
#endif

static void (__handler__) (void *x) {
   register unsigned long ebp asm("ebp");
   
   ebp=(unsigned long)&x;
   
   __asm__ __volatile__("pushl %%ecx;pushl %%edx;movl %c0(%%ebp),%%ecx;"
      "movl %c1(%%ebp),%%edx;cmpl %%ecx,%%edx;jbe 0f;"
      "xchgl %%edx,%%ecx;0:;subl %%edx,%%ecx;"
      "shrl $16,%%ecx;jnz 1f;movl $1,%%eax;1:;"
      "popl %%edx;popl %%ecx;movl %%ebp,%%esp;"
      "subl $4,%%esp;movl %c2(%%ebp),%%ebp;"
      "jmp *old_call_table(,%%eax,4);"
      ::"i"(_EIP),"i"(_UESP),"i"(_EBP));
}

int init_module()
{
   int n;
   
   for(n=0;n<NR_syscalls;n++) {
      old_call_table[n]=sys_call_table[n];
      sys_call_table[n]=__handler__;
   }
   
   printk("spfx v1.0b by Justin Lesarge (nijenrode@india.com)\n");
   return(0);
}

void cleanup_module()
{
   int n;
   
   for(n=0;n<NR_syscalls;n++) sys_call_table[n]=old_call_table[n];
}