linux-kernel - [PATCH v2] ethtool: Replace 0-length array with flexible array

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Message-Id: <20230105233420.gonna.036-kees@kernel.org>
Date:   Thu,  5 Jan 2023 15:34:21 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        kernel test robot <lkp@...el.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Sean Anderson <sean.anderson@...o.com>,
        Alexandru Tachici <alexandru.tachici@...log.com>,
        Amit Cohen <amcohen@...dia.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH v2] ethtool: Replace 0-length array with flexible array

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" <davem@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>
Cc: kernel test robot <lkp@...el.com>
Cc: Oleksij Rempel <linux@...pel-privat.de>
Cc: Sean Anderson <sean.anderson@...o.com>
Cc: Alexandru Tachici <alexandru.tachici@...log.com>
Cc: Amit Cohen <amcohen@...dia.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
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);
 };
 
 
-- 
2.34.1