libselinux:add check for malloc

Add return check for regex_data_create() to avoid NULL reference of regex_data

(gdb) bt
 #0  0x00007fbde5caec14 in pthread_mutex_init () from /usr/lib64/libc.so.6
 #1  0x00007fbde5e3a489 in regex_data_create () at regex.c:260
 SELinuxProject#2  0x00007fbde5e3a4af in regex_prepare_data (regex=regex@entry=0x7fbde4613770, pattern_string=pattern_string@entry=0x563c6799a820 "^/home$", errordata=errordata@entry=0x7ffeb83fa950) at regex.c:76
 SELinuxProject#3  0x00007fbde5e32fe6 in compile_regex (errbuf=0x0, spec=0x7fbde4613748) at label_file.h:407
 SELinuxProject#4  lookup_all (key=0x563c679974e5 "/var/log/kadmind.log", type=<optimized out>, partial=partial@entry=false, match_count=match_count@entry=0x0, rec=<optimized out>, rec=<optimized out>)
     at label_file.c:949
 SELinuxProject#5  0x00007fbde5e33350 in lookup (rec=<optimized out>, key=<optimized out>, type=<optimized out>) at label_file.c:1092
 SELinuxProject#6  0x00007fbde5e31878 in selabel_lookup_common (rec=0x563c67998cc0, translating=1, key=<optimized out>, type=<optimized out>) at label.c:167

Signed-off-by: Jie Lu <lujie54@huawei.com>
Acked-by: James Carter <jwcart2@gmail.com>

libselinux/src/regex.c

@@ -257,6 +257,9 @@ struct regex_data *regex_data_create(void)
 {
 	struct regex_data *regex_data =
 		(struct regex_data *)calloc(1, sizeof(struct regex_data));
+	if (!regex_data)
+		return NULL;
+
 	__pthread_mutex_init(&regex_data->match_mutex, NULL);
 	return regex_data;
 }