netdev - array bounds warning in xfrm_output

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Date:   Mon, 18 Jun 2018 12:10:38 -0600
From:   David Ahern <dsahern@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: array bounds warning in xfrm_output_resume

Florian:

I am seeing this warning:

$ make O=kbuild/perf -j 24 -s
In file included from /home/dsa/kernel-3.git/include/linux/kernel.h:10:0,
                 from /home/dsa/kernel-3.git/include/linux/list.h:9,
                 from /home/dsa/kernel-3.git/include/linux/module.h:9,
                 from /home/dsa/kernel-3.git/net/xfrm/xfrm_output.c:13:
/home/dsa/kernel-3.git/net/xfrm/xfrm_output.c: In function
‘xfrm_output_resume’:
/home/dsa/kernel-3.git/include/linux/compiler.h:252:20: warning: array
subscript is above array bounds [-Warray-bounds]
   __read_once_size(&(x), __u.__c, sizeof(x));  \
                    ^~~~
/home/dsa/kernel-3.git/include/linux/compiler.h:258:22: note: in
expansion of macro ‘__READ_ONCE’
 #define READ_ONCE(x) __READ_ONCE(x, 1)
                      ^~~~~~~~~~~
/home/dsa/kernel-3.git/include/linux/rcupdate.h:350:48: note: in
expansion of macro ‘READ_ONCE’
  typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
                                                ^~~~~~~~~
/home/dsa/kernel-3.git/include/linux/rcupdate.h:487:2: note: in
expansion of macro ‘__rcu_dereference_check’
  __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
  ^~~~~~~~~~~~~~~~~~~~~~~
/home/dsa/kernel-3.git/include/linux/rcupdate.h:545:28: note: in
expansion of macro ‘rcu_dereference_check’
 #define rcu_dereference(p) rcu_dereference_check(p, 0)
                            ^~~~~~~~~~~~~~~~~~~~~
/home/dsa/kernel-3.git/include/linux/netfilter.h:218:15: note: in
expansion of macro ‘rcu_dereference’
   hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
               ^~~~~~~~~~~~~~~

Line in question is the nf_hook in xfrm_output_resume.
NF_INET_POST_ROUTING = 4 which is greater than NF_ARP_NUMHOOKS = 3

I believe ef57170bbfdd6 is the commit that introduced the warning