1 // libfuzzer driver for key exchange fuzzing.
2
3
4 #include <sys/types.h>
5 #include <sys/param.h>
6 #include <stdio.h>
7 #include <stdint.h>
8 #include <stdlib.h>
9 #include <string.h>
10
11 extern "C" {
12
13 #include "includes.h"
14 #include "ssherr.h"
15 #include "ssh_api.h"
16 #include "sshbuf.h"
17 #include "packet.h"
18 #include "myproposal.h"
19 #include "xmalloc.h"
20 #include "authfile.h"
21 #include "log.h"
22
23 #include "fixed-keys.h"
24
25 // Define if you want to generate traces.
26 /* #define STANDALONE 1 */
27
28 static int prepare_key(struct shared_state *st, int keytype, int bits);
29
30 struct shared_state {
31 size_t nkeys;
32 struct sshkey **privkeys, **pubkeys;
33 };
34
35 struct test_state {
36 struct sshbuf *smsgs, *cmsgs; /* output, for standalone mode */
37 struct sshbuf *sin, *cin; /* input; setup per-test in do_kex_with_key */
38 struct sshbuf *s_template, *c_template; /* main copy of input */
39 };
40
41 static int
do_send_and_receive(struct ssh * from,struct ssh * to,struct sshbuf * store,int clobber,size_t * n)42 do_send_and_receive(struct ssh *from, struct ssh *to,
43 struct sshbuf *store, int clobber, size_t *n)
44 {
45 u_char type;
46 size_t len;
47 const u_char *buf;
48 int r;
49
50 for (*n = 0;; (*n)++) {
51 if ((r = ssh_packet_next(from, &type)) != 0) {
52 debug_fr(r, "ssh_packet_next");
53 return r;
54 }
55 if (type != 0)
56 return 0;
57 buf = ssh_output_ptr(from, &len);
58 debug_f("%zu%s", len, clobber ? " ignore" : "");
59 if (len == 0)
60 return 0;
61 if ((r = ssh_output_consume(from, len)) != 0) {
62 debug_fr(r, "ssh_output_consume");
63 return r;
64 }
65 if (store != NULL && (r = sshbuf_put(store, buf, len)) != 0) {
66 debug_fr(r, "sshbuf_put");
67 return r;
68 }
69 if (!clobber && (r = ssh_input_append(to, buf, len)) != 0) {
70 debug_fr(r, "ssh_input_append");
71 return r;
72 }
73 }
74 }
75
76 static int
run_kex(struct test_state * ts,struct ssh * client,struct ssh * server)77 run_kex(struct test_state *ts, struct ssh *client, struct ssh *server)
78 {
79 int r = 0;
80 size_t cn, sn;
81
82 /* If fuzzing, replace server/client input */
83 if (ts->sin != NULL) {
84 if ((r = ssh_input_append(server, sshbuf_ptr(ts->sin),
85 sshbuf_len(ts->sin))) != 0) {
86 error_fr(r, "ssh_input_append");
87 return r;
88 }
89 sshbuf_reset(ts->sin);
90 }
91 if (ts->cin != NULL) {
92 if ((r = ssh_input_append(client, sshbuf_ptr(ts->cin),
93 sshbuf_len(ts->cin))) != 0) {
94 error_fr(r, "ssh_input_append");
95 return r;
96 }
97 sshbuf_reset(ts->cin);
98 }
99 while (!server->kex->done || !client->kex->done) {
100 cn = sn = 0;
101 debug_f("S:");
102 if ((r = do_send_and_receive(server, client,
103 ts->smsgs, ts->cin != NULL, &sn)) != 0) {
104 debug_fr(r, "S->C");
105 break;
106 }
107 debug_f("C:");
108 if ((r = do_send_and_receive(client, server,
109 ts->cmsgs, ts->sin != NULL, &cn)) != 0) {
110 debug_fr(r, "C->S");
111 break;
112 }
113 if (cn == 0 && sn == 0) {
114 debug_f("kex stalled");
115 r = SSH_ERR_PROTOCOL_ERROR;
116 break;
117 }
118 }
119 debug_fr(r, "done");
120 return r;
121 }
122
123 static void
store_key(struct shared_state * st,struct sshkey * pubkey,struct sshkey * privkey)124 store_key(struct shared_state *st, struct sshkey *pubkey,
125 struct sshkey *privkey)
126 {
127 if (st == NULL || pubkey->type < 0 || pubkey->type > INT_MAX ||
128 privkey->type != pubkey->type ||
129 ((size_t)pubkey->type < st->nkeys &&
130 st->pubkeys[pubkey->type] != NULL))
131 abort();
132 if ((size_t)pubkey->type >= st->nkeys) {
133 st->pubkeys = (struct sshkey **)xrecallocarray(st->pubkeys,
134 st->nkeys, pubkey->type + 1, sizeof(*st->pubkeys));
135 st->privkeys = (struct sshkey **)xrecallocarray(st->privkeys,
136 st->nkeys, privkey->type + 1, sizeof(*st->privkeys));
137 st->nkeys = privkey->type + 1;
138 }
139 debug_f("store %s at %d", sshkey_ssh_name(pubkey), pubkey->type);
140 st->pubkeys[pubkey->type] = pubkey;
141 st->privkeys[privkey->type] = privkey;
142 }
143
144 static int
prepare_keys(struct shared_state * st)145 prepare_keys(struct shared_state *st)
146 {
147 if (prepare_key(st, KEY_RSA, 2048) != 0 ||
148 prepare_key(st, KEY_DSA, 1024) != 0 ||
149 prepare_key(st, KEY_ECDSA, 256) != 0 ||
150 prepare_key(st, KEY_ED25519, 256) != 0) {
151 error_f("key prepare failed");
152 return -1;
153 }
154 return 0;
155 }
156
157 static struct sshkey *
get_pubkey(struct shared_state * st,int keytype)158 get_pubkey(struct shared_state *st, int keytype)
159 {
160 if (st == NULL || keytype < 0 || (size_t)keytype >= st->nkeys ||
161 st->pubkeys == NULL || st->pubkeys[keytype] == NULL)
162 abort();
163 return st->pubkeys[keytype];
164 }
165
166 static struct sshkey *
get_privkey(struct shared_state * st,int keytype)167 get_privkey(struct shared_state *st, int keytype)
168 {
169 if (st == NULL || keytype < 0 || (size_t)keytype >= st->nkeys ||
170 st->privkeys == NULL || st->privkeys[keytype] == NULL)
171 abort();
172 return st->privkeys[keytype];
173 }
174
175 static int
do_kex_with_key(struct shared_state * st,struct test_state * ts,const char * kex,int keytype)176 do_kex_with_key(struct shared_state *st, struct test_state *ts,
177 const char *kex, int keytype)
178 {
179 struct ssh *client = NULL, *server = NULL;
180 struct sshkey *privkey = NULL, *pubkey = NULL;
181 struct sshbuf *state = NULL;
182 struct kex_params kex_params;
183 const char *ccp, *proposal[PROPOSAL_MAX] = { KEX_CLIENT };
184 char *myproposal[PROPOSAL_MAX] = {0}, *keyname = NULL;
185 int i, r;
186
187 ts->cin = ts->sin = NULL;
188 if (ts->c_template != NULL &&
189 (ts->cin = sshbuf_fromb(ts->c_template)) == NULL)
190 abort();
191 if (ts->s_template != NULL &&
192 (ts->sin = sshbuf_fromb(ts->s_template)) == NULL)
193 abort();
194
195 pubkey = get_pubkey(st, keytype);
196 privkey = get_privkey(st, keytype);
197 keyname = xstrdup(sshkey_ssh_name(privkey));
198 if (ts->cin != NULL) {
199 debug_f("%s %s clobber client %zu", kex, keyname,
200 sshbuf_len(ts->cin));
201 } else if (ts->sin != NULL) {
202 debug_f("%s %s clobber server %zu", kex, keyname,
203 sshbuf_len(ts->sin));
204 } else
205 debug_f("%s %s noclobber", kex, keyname);
206
207 for (i = 0; i < PROPOSAL_MAX; i++) {
208 ccp = proposal[i];
209 #ifdef CIPHER_NONE_AVAIL
210 if (i == PROPOSAL_ENC_ALGS_CTOS || i == PROPOSAL_ENC_ALGS_STOC)
211 ccp = "none";
212 #endif
213 if (i == PROPOSAL_SERVER_HOST_KEY_ALGS)
214 ccp = keyname;
215 else if (i == PROPOSAL_KEX_ALGS && kex != NULL)
216 ccp = kex;
217 if ((myproposal[i] = strdup(ccp)) == NULL) {
218 error_f("strdup prop %d", i);
219 goto fail;
220 }
221 }
222 memcpy(kex_params.proposal, myproposal, sizeof(myproposal));
223 if ((r = ssh_init(&client, 0, &kex_params)) != 0) {
224 error_fr(r, "init client");
225 goto fail;
226 }
227 if ((r = ssh_init(&server, 1, &kex_params)) != 0) {
228 error_fr(r, "init server");
229 goto fail;
230 }
231 if ((r = ssh_add_hostkey(server, privkey)) != 0 ||
232 (r = ssh_add_hostkey(client, pubkey)) != 0) {
233 error_fr(r, "add hostkeys");
234 goto fail;
235 }
236 if ((r = run_kex(ts, client, server)) != 0) {
237 error_fr(r, "kex");
238 goto fail;
239 }
240 /* XXX rekex, set_state, etc */
241 fail:
242 for (i = 0; i < PROPOSAL_MAX; i++)
243 free(myproposal[i]);
244 sshbuf_free(ts->sin);
245 sshbuf_free(ts->cin);
246 sshbuf_free(state);
247 ssh_free(client);
248 ssh_free(server);
249 free(keyname);
250 return r;
251 }
252
253 static int
prepare_key(struct shared_state * st,int kt,int bits)254 prepare_key(struct shared_state *st, int kt, int bits)
255 {
256 const char *pubstr = NULL;
257 const char *privstr = NULL;
258 char *tmp, *cp;
259 struct sshkey *privkey = NULL, *pubkey = NULL;
260 struct sshbuf *b = NULL;
261 int r;
262
263 switch (kt) {
264 case KEY_RSA:
265 pubstr = PUB_RSA;
266 privstr = PRIV_RSA;
267 break;
268 case KEY_DSA:
269 pubstr = PUB_DSA;
270 privstr = PRIV_DSA;
271 break;
272 case KEY_ECDSA:
273 pubstr = PUB_ECDSA;
274 privstr = PRIV_ECDSA;
275 break;
276 case KEY_ED25519:
277 pubstr = PUB_ED25519;
278 privstr = PRIV_ED25519;
279 break;
280 default:
281 abort();
282 }
283 if ((b = sshbuf_from(privstr, strlen(privstr))) == NULL)
284 abort();
285 if ((r = sshkey_parse_private_fileblob(b, "", &privkey, NULL)) != 0) {
286 error_fr(r, "priv %d", kt);
287 abort();
288 }
289 sshbuf_free(b);
290 tmp = cp = xstrdup(pubstr);
291 if ((pubkey = sshkey_new(KEY_UNSPEC)) == NULL)
292 abort();
293 if ((r = sshkey_read(pubkey, &cp)) != 0) {
294 error_fr(r, "pub %d", kt);
295 abort();
296 }
297 free(tmp);
298
299 store_key(st, pubkey, privkey);
300 return 0;
301 }
302
303 #if defined(STANDALONE)
304
305 #if 0 /* use this if generating new keys to embed above */
306 static int
307 prepare_key(struct shared_state *st, int keytype, int bits)
308 {
309 struct sshkey *privkey = NULL, *pubkey = NULL;
310 int r;
311
312 if ((r = sshkey_generate(keytype, bits, &privkey)) != 0) {
313 error_fr(r, "generate");
314 abort();
315 }
316 if ((r = sshkey_from_private(privkey, &pubkey)) != 0) {
317 error_fr(r, "make pubkey");
318 abort();
319 }
320 store_key(st, pubkey, privkey);
321 return 0;
322 }
323 #endif
324
main(void)325 int main(void)
326 {
327 static struct shared_state *st;
328 struct test_state *ts;
329 const int keytypes[] = { KEY_RSA, KEY_DSA, KEY_ECDSA, KEY_ED25519, -1 };
330 const char *kextypes[] = {
331 "sntrup761x25519-sha512@openssh.com",
332 "curve25519-sha256@libssh.org",
333 "ecdh-sha2-nistp256",
334 "diffie-hellman-group1-sha1",
335 "diffie-hellman-group-exchange-sha1",
336 NULL,
337 };
338 int i, j;
339 char *path;
340 FILE *f;
341
342 log_init("kex_fuzz", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 1);
343
344 if (st == NULL) {
345 st = (struct shared_state *)xcalloc(1, sizeof(*st));
346 prepare_keys(st);
347 }
348 /* Run each kex method for each key and save client/server packets */
349 for (i = 0; keytypes[i] != -1; i++) {
350 for (j = 0; kextypes[j] != NULL; j++) {
351 ts = (struct test_state *)xcalloc(1, sizeof(*ts));
352 ts->smsgs = sshbuf_new();
353 ts->cmsgs = sshbuf_new();
354 do_kex_with_key(st, ts, kextypes[j], keytypes[i]);
355 xasprintf(&path, "S2C-%s-%s",
356 kextypes[j], sshkey_type(st->pubkeys[keytypes[i]]));
357 debug_f("%s", path);
358 if ((f = fopen(path, "wb+")) == NULL)
359 abort();
360 if (fwrite(sshbuf_ptr(ts->smsgs), 1,
361 sshbuf_len(ts->smsgs), f) != sshbuf_len(ts->smsgs))
362 abort();
363 fclose(f);
364 free(path);
365 //sshbuf_dump(ts->smsgs, stderr);
366 xasprintf(&path, "C2S-%s-%s",
367 kextypes[j], sshkey_type(st->pubkeys[keytypes[i]]));
368 debug_f("%s", path);
369 if ((f = fopen(path, "wb+")) == NULL)
370 abort();
371 if (fwrite(sshbuf_ptr(ts->cmsgs), 1,
372 sshbuf_len(ts->cmsgs), f) != sshbuf_len(ts->cmsgs))
373 abort();
374 fclose(f);
375 free(path);
376 //sshbuf_dump(ts->cmsgs, stderr);
377 sshbuf_free(ts->smsgs);
378 sshbuf_free(ts->cmsgs);
379 free(ts);
380 }
381 }
382 for (i = 0; keytypes[i] != -1; i++) {
383 xasprintf(&path, "%s.priv",
384 sshkey_type(st->privkeys[keytypes[i]]));
385 debug_f("%s", path);
386 if (sshkey_save_private(st->privkeys[keytypes[i]], path,
387 "", "", SSHKEY_PRIVATE_OPENSSH, NULL, 0) != 0)
388 abort();
389 free(path);
390 xasprintf(&path, "%s.pub",
391 sshkey_type(st->pubkeys[keytypes[i]]));
392 debug_f("%s", path);
393 if (sshkey_save_public(st->pubkeys[keytypes[i]], path, "") != 0)
394 abort();
395 free(path);
396 }
397 }
398 #else /* !STANDALONE */
399 static void
do_kex(struct shared_state * st,struct test_state * ts,const char * kex)400 do_kex(struct shared_state *st, struct test_state *ts, const char *kex)
401 {
402 do_kex_with_key(st, ts, kex, KEY_RSA);
403 do_kex_with_key(st, ts, kex, KEY_DSA);
404 do_kex_with_key(st, ts, kex, KEY_ECDSA);
405 do_kex_with_key(st, ts, kex, KEY_ED25519);
406 }
407
408 static void
kex_tests(struct shared_state * st,struct test_state * ts)409 kex_tests(struct shared_state *st, struct test_state *ts)
410 {
411 do_kex(st, ts, "sntrup761x25519-sha512@openssh.com");
412 do_kex(st, ts, "curve25519-sha256@libssh.org");
413 do_kex(st, ts, "ecdh-sha2-nistp256");
414 do_kex(st, ts, "diffie-hellman-group1-sha1");
415 do_kex(st, ts, "diffie-hellman-group-exchange-sha1");
416 }
417
LLVMFuzzerTestOneInput(const uint8_t * data,size_t size)418 int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
419 {
420 static struct shared_state *st;
421 struct test_state *ts;
422 u_char crbuf[SSH_MAX_PRE_BANNER_LINES * 4];
423 u_char zbuf[4096] = {0};
424 static LogLevel loglevel = SYSLOG_LEVEL_INFO;
425
426 if (st == NULL) {
427 if (getenv("DEBUG") != NULL || getenv("KEX_FUZZ_DEBUG") != NULL)
428 loglevel = SYSLOG_LEVEL_DEBUG3;
429 log_init("kex_fuzz",
430 loglevel, SYSLOG_FACILITY_AUTH, 1);
431 st = (struct shared_state *)xcalloc(1, sizeof(*st));
432 prepare_keys(st);
433 }
434
435 /* Ensure that we can complete (fail) banner exchange at least */
436 memset(crbuf, '\n', sizeof(crbuf));
437
438 ts = (struct test_state *)xcalloc(1, sizeof(*ts));
439 if ((ts->s_template = sshbuf_new()) == NULL ||
440 sshbuf_put(ts->s_template, data, size) != 0 ||
441 sshbuf_put(ts->s_template, crbuf, sizeof(crbuf)) != 0 ||
442 sshbuf_put(ts->s_template, zbuf, sizeof(zbuf)) != 0)
443 abort();
444 kex_tests(st, ts);
445 sshbuf_free(ts->s_template);
446 free(ts);
447
448 ts = (struct test_state *)xcalloc(1, sizeof(*ts));
449 if ((ts->c_template = sshbuf_new()) == NULL ||
450 sshbuf_put(ts->c_template, data, size) != 0 ||
451 sshbuf_put(ts->c_template, crbuf, sizeof(crbuf)) != 0 ||
452 sshbuf_put(ts->c_template, zbuf, sizeof(zbuf)) != 0)
453 abort();
454 kex_tests(st, ts);
455 sshbuf_free(ts->c_template);
456 free(ts);
457
458 return 0;
459 }
460 #endif /* STANDALONE */
461 } /* extern "C" */
462