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Date: Mon, 17 Feb 2020 15:44:23 -0600 From: "Gustavo A. R. Silva" <gustavo@...eddedor.com> To: Pablo Neira Ayuso <pablo@...filter.org>, Jozsef Kadlecsik <kadlec@...filter.org>, Florian Westphal <fw@...len.de>, Roopa Prabhu <roopa@...ulusnetworks.com>, Nikolay Aleksandrov <nikolay@...ulusnetworks.com>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org> Cc: netfilter-devel@...r.kernel.org, coreteam@...filter.org, bridge@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, "Gustavo A. R. Silva" <gustavo@...eddedor.com> Subject: [PATCH][next] netfilter: ebtables: Replace zero-length array with flexible-array member The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com> --- net/bridge/netfilter/ebtables.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index e1256e03a9a8..78db58c7aec2 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -1561,7 +1561,7 @@ struct compat_ebt_entry_mwt { compat_uptr_t ptr; } u; compat_uint_t match_size; - compat_uint_t data[0] __attribute__ ((aligned (__alignof__(struct compat_ebt_replace)))); + compat_uint_t data[] __aligned(__alignof__(struct compat_ebt_replace)); }; /* account for possible padding between match_size and ->data */ -- 2.25.0
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