In function sfb_dump() at net/sched/sch_sfb.c:542, the call to nla_nest_start() at line 559 may return a NULL pointer, thus variable opts may refer to NULL. So an invalid memory access may be triggered when nla_nest_end() is called at line 561, as there is no checking of variable opts against NULL before pointer dereference in the callee nla_nest_end().
The related code snippets in sfb_dump() and nla_nest_end() are as following.
sfb_dump() @@net/sched/sch_sfb.c:559
 559        opts = nla_nest_start(skb, TCA_OPTIONS);
 560        NLA_PUT(skb, TCA_SFB_PARMS, sizeof(opt), &opt);
 561        return nla_nest_end(skb, opts);
nla_nest_end() @@include/net/netlink.h:1018
1018 static inline int nla_nest_end(struct sk_buff *skb, struct nlattr *start)
1019 {
1020        start->nla_len = skb_tail_pointer(skb) - (unsigned char *)start;
1021        return skb->len;
1022 }

Generally, the return value shall be checked against NULL before used. Like the following codes in another function of the same driver.
cbq_dump_class() @@net/sched/sch_cbq.c:1589
1589        nest = nla_nest_start(skb, TCA_OPTIONS);
1590        if (nest == NULL)
1591                goto nla_put_failure;
1592        if (cbq_dump_attr(skb, cl) < 0)
1593                goto nla_put_failure;
1594        nla_nest_end(skb, nest);