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

Signed-off-by: Arthur Chan <arthur.chan@adalogics.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, and 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;
+}