fuzz: add new oss-fuzz fuzzer for date.c / date.h

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -750,6 +750,7 @@ SCRIPTS = $(SCRIPT_SH_GEN) \
 ETAGS_TARGET = TAGS
 
 FUZZ_OBJS += oss-fuzz/fuzz-commit-graph.o
+FUZZ_OBJS += oss-fuzz/fuzz-date.o
 FUZZ_OBJS += oss-fuzz/fuzz-pack-headers.o
 FUZZ_OBJS += oss-fuzz/fuzz-pack-idx.o
 .PHONY: fuzz-objs

oss-fuzz/.gitignore

@@ -1,3 +1,4 @@
 fuzz-commit-graph
+fuzz-date
 fuzz-pack-headers
 fuzz-pack-idx

oss-fuzz/fuzz-date.c

@@ -0,0 +1,49 @@
+#include "git-compat-util.h"
+#include "date.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	int local;
+	int num;
+	char *str;
+	int16_t tz;
+	timestamp_t ts;
+	enum date_mode_type dmtype;
+	struct date_mode *dm;
+
+	if (size <= 4)
+		/*
+		 * we use the first byte to fuzz dmtype and the
+		 * second byte to fuzz local, then the next two
+		 * bytes to fuzz tz offset. The remainder
+		 * (at least one byte) is fed as input to
+		 * approxidate_careful().
+		 */
+		return 0;
+
+	local = !!(*data++ & 0x10);
+	num = *data++ % DATE_UNIX;
+	if (num >= DATE_STRFTIME)
+		num++;
+	dmtype = (enum date_mode_type)num;
+	size -= 2;
+
+	tz = *data++;
+	tz = (tz << 8) | *data++;
+	size -= 2;
+
+	str = xmemdupz(data, size);
+
+	ts = approxidate_careful(str, &num);
+	free(str);
+
+	dm = date_mode_from_type(dmtype);
+	dm->local = local;
+	show_date(ts, (int)tz, dm);
+
+	date_mode_release(dm);
+
+	return 0;
+}