Re: [PATCH nf-next,v2] netfilter: nft_fwd_netdev: allow to forward packets via neighbour layer

[kbuild test robot]

Hi Pablo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on nf/master]
[also build test WARNING on v4.17-rc7 next-20180531]
[if your patch is applied to the wrong git tree, please drop us a note to help 
improve the system]

url:    
https://github.com/0day-ci/linux/commits/Pablo-Neira-Ayuso/netfilter-nft_fwd_netdev-allow-to-forward-packets-via-neighbour-layer/20180601-093630
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf.git master
config: i386-allmodconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   net/netfilter/nft_fwd_netdev.c: In function 'nft_fwd_neigh_eval':
>> net/netfilter/nft_fwd_netdev.c:130:2: warning: 'neigh_table' may be used 
>> uninitialized in this function [-Wmaybe-uninitialized]
     neigh_xmit(neigh_table, dev, addr, skb);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

vim +/neigh_table +130 net/netfilter/nft_fwd_netdev.c

    76  
    77  static void nft_fwd_neigh_eval(const struct nft_expr *expr,
    78                                struct nft_regs *regs,
    79                                const struct nft_pktinfo *pkt)
    80  {
    81          struct nft_fwd_neigh *priv = nft_expr_priv(expr);
    82          void *addr = &regs->data[priv->sreg_addr];
    83          int oif = regs->data[priv->sreg_dev];
    84          unsigned int verdict = NF_STOLEN;
    85          struct sk_buff *skb = pkt->skb;
    86          struct net_device *dev;
    87          int neigh_table;
    88  
    89          dev = dev_get_by_index_rcu(nft_net(pkt), oif);
    90          if (dev == NULL)
    91                  return;
    92  
    93          skb->dev = dev;
    94  
    95          switch (priv->nfproto) {
    96          case NFPROTO_IPV4: {
    97                  struct iphdr *iph;
    98  
    99                  if (skb->protocol != htons(ETH_P_IP)) {
   100                          verdict = NFT_BREAK;
   101                          goto out;
   102                  }
   103                  if (skb_try_make_writable(skb, sizeof(*iph))) {
   104                          verdict = NF_DROP;
   105                          goto out;
   106                  }
   107                  iph = ip_hdr(skb);
   108                  ip_decrease_ttl(iph);
   109                  neigh_table = NEIGH_ARP_TABLE;
   110                  break;
   111                  }
   112          case NFPROTO_IPV6: {
   113                  struct ipv6hdr *ip6h;
   114  
   115                  if (skb->protocol != htons(ETH_P_IPV6)) {
   116                          verdict = NFT_BREAK;
   117                          goto out;
   118                  }
   119                  if (skb_try_make_writable(skb, sizeof(*ip6h))) {
   120                          verdict = NF_DROP;
   121                          goto out;
   122                  }
   123                  ip6h = ipv6_hdr(skb);
   124                  ip6h->hop_limit--;
   125                  neigh_table = NEIGH_ND_TABLE;
   126                  break;
   127                  }
   128          }
   129  
 > 130          neigh_xmit(neigh_table, dev, addr, skb);
   131  out:
   132          regs->verdict.code = verdict;
   133  }
   134  

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0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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