From dfd29588ce4fc0e0c2955ae229552604595b3277 Mon Sep 17 00:00:00 2001
From: Matt Johnston <matt@ucc.asn.au>
Date: Sat, 14 Dec 2024 21:39:08 +0800
Subject: [PATCH] Add fuzzers for sntrup

Use separate fuzzers for client vs server since KEMs have
an asymmetric API.
---
 Makefile.in                 |  3 +-
 fuzz/fuzzer-kexsntrup-cli.c | 55 +++++++++++++++++++++++++++++++++++++
 fuzz/fuzzer-kexsntrup-srv.c | 54 ++++++++++++++++++++++++++++++++++++
 3 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 fuzz/fuzzer-kexsntrup-cli.c
 create mode 100644 fuzz/fuzzer-kexsntrup-srv.c

diff --git a/Makefile.in b/Makefile.in
index 979a763b..62bfe0bf 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -297,7 +297,8 @@ check: lint
 # list of fuzz targets
 FUZZ_TARGETS=fuzzer-preauth fuzzer-pubkey fuzzer-verify fuzzer-preauth_nomaths \
 	fuzzer-kexdh fuzzer-kexecdh fuzzer-kexcurve25519 fuzzer-client fuzzer-client_nomaths \
-	fuzzer-postauth_nomaths fuzzer-cliconf
+	fuzzer-postauth_nomaths fuzzer-cliconf \
+	fuzzer-kexsntrup-srv fuzzer-kexsntrup-cli
 
 FUZZER_OPTIONS = $(addsuffix .options, $(FUZZ_TARGETS))
 FUZZ_OBJS = $(addprefix fuzz/,$(addsuffix .o,$(FUZZ_TARGETS))) \
diff --git a/fuzz/fuzzer-kexsntrup-cli.c b/fuzz/fuzzer-kexsntrup-cli.c
new file mode 100644
index 00000000..971fa4b7
--- /dev/null
+++ b/fuzz/fuzzer-kexsntrup-cli.c
@@ -0,0 +1,55 @@
+#include "fuzz.h"
+#include "session.h"
+#include "fuzz-wrapfd.h"
+#include "debug.h"
+#include "runopts.h"
+#include "algo.h"
+
+static struct key_context* keep_newkeys = NULL;
+
+static void setup() __attribute__((constructor));
+static void setup() {
+	fuzz_common_setup();
+	fuzz_cli_setup();
+
+	keep_newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
+	keep_newkeys->algo_kex = fuzz_get_algo(sshkex, "sntrup761x25519-sha512");
+}
+
+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) {
+		/* Arbitrary key to write into a buffer */
+		sign_key *hostkey = cli_opts.privkeys->first;
+		ses.newkeys = keep_newkeys;
+
+		struct kex_pqhybrid_param *param = gen_kexpqhybrid_param();
+
+		buffer * ecdh_qs = buf_getstringbuf(fuzz.input);
+
+		ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS);
+		kexpqhybrid_comb_key(param, ecdh_qs, hostkey);
+
+		free_kexpqhybrid_param(param);
+
+		buf_free(ses.dh_K_bytes);
+		buf_free(ecdh_qs);
+
+		buf_free(ses.hash);
+		buf_free(ses.session_id);
+		/* kexhashbuf is freed in kexpqhybrid_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;
+}
diff --git a/fuzz/fuzzer-kexsntrup-srv.c b/fuzz/fuzzer-kexsntrup-srv.c
new file mode 100644
index 00000000..0e60ea20
--- /dev/null
+++ b/fuzz/fuzzer-kexsntrup-srv.c
@@ -0,0 +1,54 @@
+#include "fuzz.h"
+#include "session.h"
+#include "fuzz-wrapfd.h"
+#include "debug.h"
+#include "runopts.h"
+#include "algo.h"
+
+static struct key_context* keep_newkeys = NULL;
+
+static void setup() __attribute__((constructor));
+static void setup() {
+	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, "sntrup761x25519-sha512");
+	keep_newkeys->algo_hostkey = DROPBEAR_SIGNKEY_ED25519;
+}
+
+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) {
+		ses.newkeys = keep_newkeys;
+
+		struct kex_pqhybrid_param *param = gen_kexpqhybrid_param();
+
+		buffer * ecdh_qc = buf_getstringbuf(fuzz.input);
+
+		ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS);
+		kexpqhybrid_comb_key(param, ecdh_qc, svr_opts.hostkey);
+
+		free_kexpqhybrid_param(param);
+
+		buf_free(ses.dh_K_bytes);
+		buf_free(ecdh_qc);
+
+		buf_free(ses.hash);
+		buf_free(ses.session_id);
+		/* kexhashbuf is freed in kexpqhybrid_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;
+}