--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/fuzz/fuzzer-kexdh.c	Fri Oct 23 23:10:20 2020 +0800
@@ -0,0 +1,76 @@
+#include "fuzz.h"
+#include "session.h"
+#include "fuzz-wrapfd.h"
+#include "debug.h"
+#include "runopts.h"
+#include "algo.h"
+#include "bignum.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+	static int once = 0;
+	static struct key_context* keep_newkeys = NULL;
+	/* number of generated parameters is limited by the timeout for the first run.
+	   TODO move this to the libfuzzer initialiser function instead if the timeout
+	   doesn't apply there */
+	#define NUM_PARAMS 20
+	static struct kex_dh_param *dh_params[NUM_PARAMS];
+
+	if (!once) {
+		fuzz_common_setup();
+		fuzz_svr_setup();
+
+		keep_newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
+		keep_newkeys->algo_kex = fuzz_get_algo(sshkex, "diffie-hellman-group14-sha256");
+		keep_newkeys->algo_hostkey = DROPBEAR_SIGNKEY_ECDSA_NISTP256;
+		ses.newkeys = keep_newkeys;
+
+		/* Pre-generate parameters */
+		int i;
+		for (i = 0; i < NUM_PARAMS; i++) {
+			dh_params[i] = gen_kexdh_param();
+		}
+
+		once = 1;
+	}
+
+	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_NORMAL_DH */
+		ses.newkeys = keep_newkeys;
+
+		/* Choose from the collection of ecdh params */
+		unsigned int e = buf_getint(fuzz.input);
+		struct kex_dh_param * dh_param = dh_params[e % NUM_PARAMS];
+
+		DEF_MP_INT(dh_e);
+		m_mp_init(&dh_e);
+		if (buf_getmpint(fuzz.input, &dh_e) != DROPBEAR_SUCCESS) {
+			dropbear_exit("Bad kex value");
+		}
+
+		ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS);
+		kexdh_comb_key(dh_param, &dh_e, svr_opts.hostkey);
+
+		mp_clear(ses.dh_K);
+		m_free(ses.dh_K);
+		mp_clear(&dh_e);
+
+		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;
+}