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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id o13-20020a63e34d000000b004a3510effa5sm78223pgj.65.2023.01.05.20.22.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Jan 2023 20:22:18 -0800 (PST) Date: Thu, 5 Jan 2023 20:22:17 -0800 From: Kees Cook To: Vincent MAILHOL Cc: "David S. Miller" , Jakub Kicinski , Andrew Lunn , kernel test robot , Oleksij Rempel , Sean Anderson , Alexandru Tachici , Amit Cohen , "Gustavo A. R. Silva" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2] ethtool: Replace 0-length array with flexible array Message-ID: <202301052021.5AEF89CB@keescook> References: <20230105233420.gonna.036-kees@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Jan 06, 2023 at 09:55:30AM +0900, Vincent MAILHOL wrote: > On Fri. 6 Jan 2023 at 08:34, Kees Cook wrote: > > Zero-length arrays are deprecated[1]. Replace struct ethtool_rxnfc's > > "rule_locs" 0-length array with a flexible array. Detected with GCC 13, > > using -fstrict-flex-arrays=3: > > > > net/ethtool/common.c: In function 'ethtool_get_max_rxnfc_channel': > > net/ethtool/common.c:558:55: warning: array subscript i is outside array bounds of '__u32[0]' {aka 'unsigned int[]'} [-Warray-bounds=] > > 558 | .fs.location = info->rule_locs[i], > > | ~~~~~~~~~~~~~~~^~~ > > In file included from include/linux/ethtool.h:19, > > from include/uapi/linux/ethtool_netlink.h:12, > > from include/linux/ethtool_netlink.h:6, > > from net/ethtool/common.c:3: > > include/uapi/linux/ethtool.h:1186:41: note: while referencing > > 'rule_locs' > > 1186 | __u32 rule_locs[0]; > > | ^~~~~~~~~ > > > > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays > > > > Cc: "David S. Miller" > > Cc: Jakub Kicinski > > Cc: Andrew Lunn > > Cc: kernel test robot > > Cc: Oleksij Rempel > > Cc: Sean Anderson > > Cc: Alexandru Tachici > > Cc: Amit Cohen > > Cc: "Gustavo A. R. Silva" > > Cc: Vincent Mailhol > > Cc: netdev@vger.kernel.org > > Signed-off-by: Kees Cook > > --- > > v2: resend, this time without missing netdev CC. :) > > --- > > include/uapi/linux/ethtool.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h > > index 58e587ba0450..9b97b3e0ec1f 100644 > > --- a/include/uapi/linux/ethtool.h > > +++ b/include/uapi/linux/ethtool.h > > @@ -1183,7 +1183,7 @@ struct ethtool_rxnfc { > > __u32 rule_cnt; > > __u32 rss_context; > > }; > > - __u32 rule_locs[0]; > > + __DECLARE_FLEX_ARRAY(__u32, rule_locs); > > Can't this simply be a C99 flexible array member? > > __u32 rule_locs[]; > > As far as I understand, __DECLARE_FLEX_ARRAY() is a hack to allow the > declaration of a flexible array within unions (which otherwise do not > accept flexible array members). However, ethtool_rxnfc being a struct, > I do not see the need for __DECLARE_FLEX_ARRAY() here. Good point -- I think my eyes scanned through the "union" above and I just jumped at using __DECLARE_FLEX_ARRAY. I'll send a v2. Thanks! -- Kees Cook