/*
 * this program tells if an ELF has a PT_GNU_STACK marker, and can set it to rw so that it can be loaded in a PaX-enhanced kernel
 *
 * Author: Yoann Guillot, 03/2007
 * Licence: public domain
 */

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

typedef struct {
	unsigned long	p_type;
	unsigned long	p_offset;
	unsigned long	p_vaddr;
	unsigned long	p_paddr;
	unsigned long	p_filesz;
	unsigned long	p_memsz;
	unsigned long	p_flags;
	unsigned long	p_align;
} phdr;

int main(int argc, char **argv)
{
	if (argc < 2) {
		fprintf(stderr, "usage: fix [--checkonly] <filename>\n");
		exit(1);
	}
	int justsee = (argc > 2);

	printf("%s: ", argv[argc-1]);

	int fd = open(argv[argc-1], (justsee ? O_RDONLY : O_RDWR));
	if (fd == -1) {
		perror("open");
		exit(1);
	}

	unsigned long len = lseek(fd, 0, SEEK_END);

	char *ptr = mmap(0, len, PROT_READ | (justsee ? 0 : PROT_WRITE), MAP_SHARED, fd, 0);
	if (ptr == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}
	close(fd);

	if (memcmp(ptr, "\x7f" "ELF", 4)) {
		printf("not an ELF file\n");
		exit(0);
	}

	unsigned long off;
	if (!(off = *(unsigned long*)(ptr + 28))) {
		printf("not an executable ELF\n");
		exit(0);
	}
	len = *(unsigned short*)(ptr + 44);

	unsigned long i;
	int found = 0;
	phdr *hdr = (phdr*)(ptr + off);
	for (i=0 ; i<len ; i++) {
		if (hdr[i].p_type == 0x6474e551) {
			found = 1;
			int hasx = hdr[i].p_flags & 1;
			printf("pt_gnu_stack: %s\n", hasx ? "rwx" : "rw");
			if (!justsee)
				hdr[i].p_flags &= ~1;
		}
	}
	if (!found)
		printf("no pt_gnu_stack entry, defaults to rwx, you should recompile\n");

	return 0;
}