Function nal_reserve() will return NULL if the tailroom of skb is insufficient, so the return value shall be checked against NULL before used. But in function cgroupstats_user_cmd(), the return value of nla_reserve()(called at kernel/taskstats.c:430) is used without NULL check.
The related codes are as following.
cgroupstats_user_cmd @@kernel/taskstats.c:430
 430        na = nla_reserve(rep_skb, CGROUPSTATS_TYPE_CGROUP_STATS,
 431                                sizeof(struct cgroupstats));
 432        stats = nla_data(na);
 433        memset(stats, 0, sizeof(*stats));

Generally, the return value of nla_reserve() is checked against NULL. For example, in function mk_reply() in the same file with cgroupstats_user_cmd().
mk_reply @@kernel/taskstats.c:393
 393        ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats));
 394        if (!ret)
 395                goto err;
 396        nla_nest_end(skb, na);
 397
 398        return nla_data(ret);


Thank you

RUC_Soft_Sec