From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=embeddedor.com; s=default; h=Content-Type:MIME-Version:Message-ID:Subject: Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=8exBLdInKXUzJxq+ZuAOxKExTTscVDb1+bUsC6sGG8g=; b=HgN+9rsp3fFCj0fJUhjufn2/l7 VUbRynRSy0CAxMQY1KjfA6V0LtIYanqWDAcf8yWC0eCA4k6KrY0nHZXuU/xZc13RL7fkTFbpblB9Z oaw0tEO4v2iCjRJSKPg7FVGlJmBpyn54igDPdhEvFipu6bdIypiYf2GXKs6TVHrC6ONCP579pTBsD k6d1SyEurDwqrzaiQ1aIEJb6Ekg+EqhR2woGKuNkFF0iOLmuHVv8PsANnufrSfgeIw47Z2AM++650 z398+1TN/CWW5k09Ld5ZremaZw19BRvbwk+wOE0VJUTDklJDkNpaX6tXERWgdq/NvwlKLQ1s2lOvv y6pqb2rA==; Date: Mon, 17 Feb 2020 15:44:23 -0600 From: "Gustavo A. R. Silva" Message-ID: <20200217214423.GA15008@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Bridge] [PATCH][next] netfilter: ebtables: Replace zero-length array with flexible-array member List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , Roopa Prabhu , Nikolay Aleksandrov , "David S. Miller" , Jakub Kicinski Cc: "Gustavo A. R. Silva" , netdev@vger.kernel.org, bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, coreteam@netfilter.org, netfilter-devel@vger.kernel.org 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 --- 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