fast-import: stricter parsing of integer options

Check the result from strtoul to avoid accepting arguments like
--depth=-1 and --active-branches=foo,bar,baz.

Requested-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fast-import.c

@@ -2746,16 +2746,25 @@ static void option_date_format(const char *fmt)
 		die("unknown --date-format argument %s", fmt);
 }
 
+static unsigned long ulong_arg(const char *option, const char *arg)
+{
+	char *endptr;
+	unsigned long rv = strtoul(arg, &endptr, 0);
+	if (strchr(arg, '-') || endptr == arg || *endptr)
+		die("%s: argument must be a non-negative integer", option);
+	return rv;
+}
+
 static void option_depth(const char *depth)
 {
-	max_depth = strtoul(depth, NULL, 0);
+	max_depth = ulong_arg("--depth", depth);
 	if (max_depth > MAX_DEPTH)
 		die("--depth cannot exceed %u", MAX_DEPTH);
 }
 
 static void option_active_branches(const char *branches)
 {
-	max_active_branches = strtoul(branches, NULL, 0);
+	max_active_branches = ulong_arg("--active-branches", branches);
 }
 
 static void option_export_marks(const char *marks)

t/t9300-fast-import.sh

@@ -1659,6 +1659,14 @@ test_expect_success 'R: unknown commandline options are rejected' '\
     test_must_fail git fast-import --non-existing-option < /dev/null
 '
 
+test_expect_success 'R: die on invalid option argument' '
+	echo "option git active-branches=-5" |
+	test_must_fail git fast-import &&
+	echo "option git depth=" |
+	test_must_fail git fast-import &&
+	test_must_fail git fast-import --depth="5 elephants" </dev/null
+'
+
 cat >input <<EOF
 option non-existing-vcs non-existing-option
 EOF