Subject: Re: [PATCH bpf-next V1 2/6] bpf: bpf_fib_lookup return MTU value as output when looked up

From: kernel test robot <[email-masked]>
Date: Wed, 7 Oct 2020 10:28:26 +0300

Hi Jesper,

url:    https://github.com/0day-ci/linux/commits/Jesper-Dangaard-Brouer/bpf-New-approach-for-BPF-MTU-handling-and-enforcement/20201007-000903
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: s390-randconfig-m031-20201002 (attached as .config)
compiler: s390-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[email-masked]>
Reported-by: Dan Carpenter <[email-masked]>

smatch warnings:
net/core/filter.c:5315 bpf_ipv4_fib_lookup() error: uninitialized symbol 'mtu'.

vim +/mtu +5315 net/core/filter.c

87f5fc7e48dd31 David Ahern            2018-05-09  5202  static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
4f74fede40df8d David Ahern            2018-05-21  5203  			       u32 flags, bool check_mtu)
87f5fc7e48dd31 David Ahern            2018-05-09  5204  {
eba618abacade7 David Ahern            2019-04-02  5205  	struct fib_nh_common *nhc;
87f5fc7e48dd31 David Ahern            2018-05-09  5206  	struct in_device *in_dev;
87f5fc7e48dd31 David Ahern            2018-05-09  5207  	struct neighbour *neigh;
87f5fc7e48dd31 David Ahern            2018-05-09  5208  	struct net_device *dev;
87f5fc7e48dd31 David Ahern            2018-05-09  5209  	struct fib_result res;
87f5fc7e48dd31 David Ahern            2018-05-09  5210  	struct flowi4 fl4;
87f5fc7e48dd31 David Ahern            2018-05-09  5211  	int err;
4f74fede40df8d David Ahern            2018-05-21  5212  	u32 mtu;
87f5fc7e48dd31 David Ahern            2018-05-09  5213  
87f5fc7e48dd31 David Ahern            2018-05-09  5214  	dev = dev_get_by_index_rcu(net, params->ifindex);
87f5fc7e48dd31 David Ahern            2018-05-09  5215  	if (unlikely(!dev))
87f5fc7e48dd31 David Ahern            2018-05-09  5216  		return -ENODEV;
87f5fc7e48dd31 David Ahern            2018-05-09  5217  
87f5fc7e48dd31 David Ahern            2018-05-09  5218  	/* verify forwarding is enabled on this interface */
87f5fc7e48dd31 David Ahern            2018-05-09  5219  	in_dev = __in_dev_get_rcu(dev);
87f5fc7e48dd31 David Ahern            2018-05-09  5220  	if (unlikely(!in_dev || !IN_DEV_FORWARD(in_dev)))
4c79579b44b187 David Ahern            2018-06-26  5221  		return BPF_FIB_LKUP_RET_FWD_DISABLED;
87f5fc7e48dd31 David Ahern            2018-05-09  5222  
87f5fc7e48dd31 David Ahern            2018-05-09  5223  	if (flags & BPF_FIB_LOOKUP_OUTPUT) {
87f5fc7e48dd31 David Ahern            2018-05-09  5224  		fl4.flowi4_iif = 1;
87f5fc7e48dd31 David Ahern            2018-05-09  5225  		fl4.flowi4_oif = params->ifindex;
87f5fc7e48dd31 David Ahern            2018-05-09  5226  	} else {
87f5fc7e48dd31 David Ahern            2018-05-09  5227  		fl4.flowi4_iif = params->ifindex;
87f5fc7e48dd31 David Ahern            2018-05-09  5228  		fl4.flowi4_oif = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5229  	}
87f5fc7e48dd31 David Ahern            2018-05-09  5230  	fl4.flowi4_tos = params->tos & IPTOS_RT_MASK;
87f5fc7e48dd31 David Ahern            2018-05-09  5231  	fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
87f5fc7e48dd31 David Ahern            2018-05-09  5232  	fl4.flowi4_flags = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5233  
87f5fc7e48dd31 David Ahern            2018-05-09  5234  	fl4.flowi4_proto = params->l4_protocol;
87f5fc7e48dd31 David Ahern            2018-05-09  5235  	fl4.daddr = params->ipv4_dst;
87f5fc7e48dd31 David Ahern            2018-05-09  5236  	fl4.saddr = params->ipv4_src;
87f5fc7e48dd31 David Ahern            2018-05-09  5237  	fl4.fl4_sport = params->sport;
87f5fc7e48dd31 David Ahern            2018-05-09  5238  	fl4.fl4_dport = params->dport;
1869e226a7b3ef David Ahern            2020-09-13  5239  	fl4.flowi4_multipath_hash = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5240  
87f5fc7e48dd31 David Ahern            2018-05-09  5241  	if (flags & BPF_FIB_LOOKUP_DIRECT) {
87f5fc7e48dd31 David Ahern            2018-05-09  5242  		u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
87f5fc7e48dd31 David Ahern            2018-05-09  5243  		struct fib_table *tb;
87f5fc7e48dd31 David Ahern            2018-05-09  5244  
87f5fc7e48dd31 David Ahern            2018-05-09  5245  		tb = fib_get_table(net, tbid);
87f5fc7e48dd31 David Ahern            2018-05-09  5246  		if (unlikely(!tb))
4c79579b44b187 David Ahern            2018-06-26  5247  			return BPF_FIB_LKUP_RET_NOT_FWDED;
87f5fc7e48dd31 David Ahern            2018-05-09  5248  
87f5fc7e48dd31 David Ahern            2018-05-09  5249  		err = fib_table_lookup(tb, &fl4, &res, FIB_LOOKUP_NOREF);
87f5fc7e48dd31 David Ahern            2018-05-09  5250  	} else {
87f5fc7e48dd31 David Ahern            2018-05-09  5251  		fl4.flowi4_mark = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5252  		fl4.flowi4_secid = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5253  		fl4.flowi4_tun_key.tun_id = 0;
87f5fc7e48dd31 David Ahern            2018-05-09  5254  		fl4.flowi4_uid = sock_net_uid(net, NULL);
87f5fc7e48dd31 David Ahern            2018-05-09  5255  
87f5fc7e48dd31 David Ahern            2018-05-09  5256  		err = fib_lookup(net, &fl4, &res, FIB_LOOKUP_NOREF);
87f5fc7e48dd31 David Ahern            2018-05-09  5257  	}
87f5fc7e48dd31 David Ahern            2018-05-09  5258  
4c79579b44b187 David Ahern            2018-06-26  5259  	if (err) {
4c79579b44b187 David Ahern            2018-06-26  5260  		/* map fib lookup errors to RTN_ type */
4c79579b44b187 David Ahern            2018-06-26  5261  		if (err == -EINVAL)
4c79579b44b187 David Ahern            2018-06-26  5262  			return BPF_FIB_LKUP_RET_BLACKHOLE;
4c79579b44b187 David Ahern            2018-06-26  5263  		if (err == -EHOSTUNREACH)
4c79579b44b187 David Ahern            2018-06-26  5264  			return BPF_FIB_LKUP_RET_UNREACHABLE;
4c79579b44b187 David Ahern            2018-06-26  5265  		if (err == -EACCES)
4c79579b44b187 David Ahern            2018-06-26  5266  			return BPF_FIB_LKUP_RET_PROHIBIT;
4c79579b44b187 David Ahern            2018-06-26  5267  
4c79579b44b187 David Ahern            2018-06-26  5268  		return BPF_FIB_LKUP_RET_NOT_FWDED;
4c79579b44b187 David Ahern            2018-06-26  5269  	}
4c79579b44b187 David Ahern            2018-06-26  5270  
4c79579b44b187 David Ahern            2018-06-26  5271  	if (res.type != RTN_UNICAST)
4c79579b44b187 David Ahern            2018-06-26  5272  		return BPF_FIB_LKUP_RET_NOT_FWDED;
87f5fc7e48dd31 David Ahern            2018-05-09  5273  
5481d73f81549e David Ahern            2019-06-03  5274  	if (fib_info_num_path(res.fi) > 1)
87f5fc7e48dd31 David Ahern            2018-05-09  5275  		fib_select_path(net, &res, &fl4, NULL);
87f5fc7e48dd31 David Ahern            2018-05-09  5276  
4f74fede40df8d David Ahern            2018-05-21  5277  	if (check_mtu) {
4f74fede40df8d David Ahern            2018-05-21  5278  		mtu = ip_mtu_from_fib_result(&res, params->ipv4_dst);
ab61fc7ee5c482 Jesper Dangaard Brouer 2020-10-06  5279  		if (params->tot_len > mtu) {
ab61fc7ee5c482 Jesper Dangaard Brouer 2020-10-06  5280  			params->mtu = mtu; /* union with tot_len */
4c79579b44b187 David Ahern            2018-06-26  5281  			return BPF_FIB_LKUP_RET_FRAG_NEEDED;
4f74fede40df8d David Ahern            2018-05-21  5282  		}
ab61fc7ee5c482 Jesper Dangaard Brouer 2020-10-06  5283  	}

"mtu" is not initialized on else path.

4f74fede40df8d David Ahern            2018-05-21  5284  
eba618abacade7 David Ahern            2019-04-02  5285  	nhc = res.nhc;
87f5fc7e48dd31 David Ahern            2018-05-09  5286  
87f5fc7e48dd31 David Ahern            2018-05-09  5287  	/* do not handle lwt encaps right now */
eba618abacade7 David Ahern            2019-04-02  5288  	if (nhc->nhc_lwtstate)
4c79579b44b187 David Ahern            2018-06-26  5289  		return BPF_FIB_LKUP_RET_UNSUPP_LWT;
87f5fc7e48dd31 David Ahern            2018-05-09  5290  
eba618abacade7 David Ahern            2019-04-02  5291  	dev = nhc->nhc_dev;
87f5fc7e48dd31 David Ahern            2018-05-09  5292  
87f5fc7e48dd31 David Ahern            2018-05-09  5293  	params->rt_metric = res.fi->fib_priority;
87f5fc7e48dd31 David Ahern            2018-05-09  5294  
87f5fc7e48dd31 David Ahern            2018-05-09  5295  	/* xdp and cls_bpf programs are run in RCU-bh so
87f5fc7e48dd31 David Ahern            2018-05-09  5296  	 * rcu_read_lock_bh is not needed here
87f5fc7e48dd31 David Ahern            2018-05-09  5297  	 */
6f5f68d05ec0f6 David Ahern            2019-04-05  5298  	if (likely(nhc->nhc_gw_family != AF_INET6)) {
6f5f68d05ec0f6 David Ahern            2019-04-05  5299  		if (nhc->nhc_gw_family)
6f5f68d05ec0f6 David Ahern            2019-04-05  5300  			params->ipv4_dst = nhc->nhc_gw.ipv4;
6f5f68d05ec0f6 David Ahern            2019-04-05  5301  
6f5f68d05ec0f6 David Ahern            2019-04-05  5302  		neigh = __ipv4_neigh_lookup_noref(dev,
6f5f68d05ec0f6 David Ahern            2019-04-05  5303  						 (__force u32)params->ipv4_dst);
6f5f68d05ec0f6 David Ahern            2019-04-05  5304  	} else {
6f5f68d05ec0f6 David Ahern            2019-04-05  5305  		struct in6_addr *dst = (struct in6_addr *)params->ipv6_dst;
6f5f68d05ec0f6 David Ahern            2019-04-05  5306  
6f5f68d05ec0f6 David Ahern            2019-04-05  5307  		params->family = AF_INET6;
6f5f68d05ec0f6 David Ahern            2019-04-05  5308  		*dst = nhc->nhc_gw.ipv6;
6f5f68d05ec0f6 David Ahern            2019-04-05  5309  		neigh = __ipv6_neigh_lookup_noref_stub(dev, dst);
6f5f68d05ec0f6 David Ahern            2019-04-05  5310  	}
6f5f68d05ec0f6 David Ahern            2019-04-05  5311  
4c79579b44b187 David Ahern            2018-06-26  5312  	if (!neigh)
4c79579b44b187 David Ahern            2018-06-26  5313  		return BPF_FIB_LKUP_RET_NO_NEIGH;
87f5fc7e48dd31 David Ahern            2018-05-09  5314  
ab61fc7ee5c482 Jesper Dangaard Brouer 2020-10-06 @5315  	return bpf_fib_set_fwd_params(params, neigh, dev, mtu);
                                                                                                                  ^^^
Uninitialized.

87f5fc7e48dd31 David Ahern            2018-05-09  5316  }

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