fuzzer-kexecdh.c

#include "fuzz.h"
#include "session.h"
#include "fuzz-wrapfd.h"
#include "debug.h"
#include "runopts.h"
#include "algo.h"
#include "bignum.h"

static const struct dropbear_kex *ecdh[3]; /* 256, 384, 521 */
static struct key_context* keep_newkeys = NULL;
/* number of generated parameters. An arbitrary limit, but will delay startup */
#define NUM_PARAMS 80
static struct kex_ecdh_param *ecdh_params[NUM_PARAMS];

static void setup() __attribute__((constructor));
// Perform initial setup here to avoid hitting timeouts on first run
static void setup() {
	fuzz_common_setup();
	fuzz_svr_setup();

	/* ses gets zeroed by fuzz_set_input */
	keep_newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
	ecdh[0] = fuzz_get_algo(sshkex, "ecdh-sha2-nistp256");
	ecdh[1] = fuzz_get_algo(sshkex, "ecdh-sha2-nistp384");
	ecdh[2] = fuzz_get_algo(sshkex, "ecdh-sha2-nistp521");
	assert(ecdh[0]);
	assert(ecdh[1]);
	assert(ecdh[2]);
	keep_newkeys->algo_hostkey = DROPBEAR_SIGNKEY_ECDSA_NISTP256;
	ses.newkeys = keep_newkeys;

	/* Pre-generate parameters */
	int i;
	for (i = 0; i < NUM_PARAMS; i++) {
		ses.newkeys->algo_kex = ecdh[i % 3];
		ecdh_params[i] = gen_kexecdh_param();
	}
}

int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {

	if (fuzz_set_input(Data, Size) == DROPBEAR_FAILURE) {
		return 0;
	}

	m_malloc_set_epoch(1);

	if (setjmp(fuzz.jmp) == 0) {
		/* Based on recv_msg_kexdh_init()/send_msg_kexdh_reply() 
		with DROPBEAR_KEX_ECDH */
		ses.newkeys = keep_newkeys;

		/* random choice of ecdh 256, 384, 521 */
		unsigned char b = buf_getbyte(fuzz.input);
		ses.newkeys->algo_kex = ecdh[b % 3];

		/* Choose from the collection of ecdh params */
		unsigned int e = buf_getint(fuzz.input);
		struct kex_ecdh_param *ecdh_param = ecdh_params[e % NUM_PARAMS];

		buffer * ecdh_qs = buf_getstringbuf(fuzz.input);

		ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS);
		kexecdh_comb_key(ecdh_param, ecdh_qs, svr_opts.hostkey);

		mp_clear(ses.dh_K);
		m_free(ses.dh_K);
		buf_free(ecdh_qs);

		buf_free(ses.hash);
		buf_free(ses.session_id);
		/* kexhashbuf is freed in kexdh_comb_key */

		m_malloc_free_epoch(1, 0);
	} else {
		m_malloc_free_epoch(1, 1);
		TRACE(("dropbear_exit longjmped"))
		/* dropbear_exit jumped here */
	}

	return 0;
}