linux-kernel - [PATCH v3 02/12] netfilter: Avoid assigning 'const' pointer to non-const pointer

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Date:   Wed, 15 Apr 2020 17:52:08 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, kernel-team@...roid.com,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH v3 02/12] netfilter: Avoid assigning 'const' pointer to non-const pointer

nf_remove_net_hook() uses WRITE_ONCE() to assign a 'const' pointer to a
'non-const' pointer. Cleanups to the implementation of WRITE_ONCE() mean
that this will give rise to a compiler warning, just like a plain old
assignment would do:

  | In file included from ./include/linux/export.h:43,
  |                  from ./include/linux/linkage.h:7,
  |                  from ./include/linux/kernel.h:8,
  |                  from net/netfilter/core.c:9:
  | net/netfilter/core.c: In function ‘nf_remove_net_hook’:
  | ./include/linux/compiler.h:216:30: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  |   *(volatile typeof(x) *)&(x) = (val);  \
  |                               ^
  | net/netfilter/core.c:379:3: note: in expansion of macro ‘WRITE_ONCE’
  |    WRITE_ONCE(orig_ops[i], &dummy_ops);
  |    ^~~~~~~~~~

Follow the pattern used elsewhere in this file and add a cast to 'void *'
to squash the warning.

Cc: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Jozsef Kadlecsik <kadlec@...filter.org>
Cc: Florian Westphal <fw@...len.de>
Cc: "David S. Miller" <davem@...emloft.net>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 net/netfilter/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 78f046ec506f..3ac7c8c1548d 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -376,7 +376,7 @@ static bool nf_remove_net_hook(struct nf_hook_entries *old,
 		if (orig_ops[i] != unreg)
 			continue;
 		WRITE_ONCE(old->hooks[i].hook, accept_all);
-		WRITE_ONCE(orig_ops[i], &dummy_ops);
+		WRITE_ONCE(orig_ops[i], (void *)&dummy_ops);
 		return true;
 	}
 
-- 
2.26.0.110.g2183baf09c-goog