#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <signal.h>
#include <sys/mman.h>

#define __USE_GNU
#include <sys/ucontext.h>

#define INIT_MODULE 0x08053a49
#define CREATE_MODULE 0x8053a48

int page_size;
unsigned char hook_char;
unsigned char *hook_at;

void insert_hook(unsigned int where)
{
	if(mprotect((void *)((where) & ~(page_size-1)), page_size, PROT_READ|PROT_WRITE|PROT_EXEC) == -1) {
		fprintf(stderr, "--> Unable to change memory protection on required page: %s\n", strerror(errno));
		exit(EXIT_FAILURE);
	}

	hook_at = (unsigned char *)(where);
	hook_char = hook_at[0];
	hook_at[0] = 0xcc;
}

void remove_hook()
{
	hook_at[0] = hook_char;
}

void dump_module(unsigned char *text)
{
	unsigned int *texti;
	FILE *f;
	int struct_size, module_size;

	texti = (unsigned int *)(text);

	struct_size = texti[0];
	module_size = texti[3];
	
	f = fopen("/tmp/module_header", "w+");
	fwrite(text, struct_size, 1, f);
	fclose(f);

	f = fopen("/tmp/module_text", "w+");
	fwrite(text + struct_size, module_size, 1, f);
	fclose(f);
}

void setup_sighandler(unsigned int *fp)
{
	struct sigaction sa;
	memset(&sa, 0, sizeof(struct sigaction));
	sa.sa_sigaction = (void *)fp;
	sa.sa_flags = SA_SIGINFO|SA_ONESHOT;
	sigaction(SIGTRAP, &sa, NULL);
}

void int3_common(ucontext_t *uc)
{
	fprintf(stderr, "--> In an int3 handler\n");
	remove_hook();
	uc->uc_mcontext.gregs[REG_EIP]--; // Restore EIP to point
					  // the appropriate place
}	

void int3_init_module(int signo, siginfo_t *si, ucontext_t *uc)
{
	unsigned char **params;
	int i;

	int3_common(uc);

	// ESP 0 = return address
	params = (unsigned long) (uc->uc_mcontext.gregs[REG_ESP] + 4);
	fprintf(stderr, "--> working our magic for %s\n", params[0]);

	dump_module(params[1]);
}

void int3_create_module(int signo, siginfo_t *si, ucontext_t *uc)
{
	int3_common(uc);

	fprintf(stderr, "--> Create module return address is 0x%08x\n", 
		uc->uc_mcontext.gregs[REG_EAX]);

	insert_hook(INIT_MODULE);
	setup_sighandler(int3_init_module);
}


void _init()
{
	page_size = getpagesize();
	insert_hook(CREATE_MODULE);
	setup_sighandler(int3_create_module);
	
}