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netfilter: avoid erronous array bounds warning 

Unfortunately some versions of gcc emit following warning:
  $ make net/xfrm/xfrm_output.o
  linux/compiler.h:252:20: warning: array subscript is above array bounds [-Warray-bounds]
  hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
                            ^~~~~~~~~~~~~~~~~~~~~
xfrm_output_resume passes skb_dst(skb)->ops->family as its 'pf' arg so compiler
can't know that we'll never access hooks_arp[].
(NFPROTO_IPV4 or NFPROTO_IPV6 are only possible cases).

Avoid this by adding an explicit WARN_ON_ONCE() check.

This patch has no effect if the family is a compile-time constant as gcc
will remove the switch() construct entirely.

Reported-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2018-09-24 14:10:04 +02:00 committed by Pablo Neira Ayuso
parent a13f814a67
commit 421c119f55
1 changed files with 2 additions and 0 deletions
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include/linux/netfilter.h
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@ -215,6 +215,8 @@ static inline int nf_hook(u_int8_t pf, unsigned int hook, struct net *net,
break;
case NFPROTO_ARP:
#ifdef CONFIG_NETFILTER_FAMILY_ARP
if (WARN_ON_ONCE(hook >= ARRAY_SIZE(net->nf.hooks_arp)))
break;
hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
#endif
break;