netdev - Re: [PATCH 4/5][next] uapi: net: arp: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <20241016034429.90455-1-kuniyu@amazon.com>
Date: Tue, 15 Oct 2024 20:44:29 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <gustavoars@...nel.org>
CC: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <dsahern@...nel.org>,
	<edumazet@...gle.com>, <kees@...nel.org>, <kuba@...nel.org>,
	<linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>, Kuniyuki Iwashima
	<kuniyu@...zon.com>
Subject: Re: [PATCH 4/5][next] uapi: net: arp: Avoid -Wflex-array-member-not-at-end warnings

From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Date: Tue, 15 Oct 2024 18:32:43 -0600
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Address the following warnings by changing the type of the middle struct
> members in a couple of composite structs, which are currently causing
> trouble, from `struct sockaddr` to `struct sockaddr_legacy`. Note that
> the latter struct doesn't contain a flexible-array member.
> 
> include/uapi/linux/if_arp.h:118:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:119:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:121:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:126:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:127:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Also, update some related code, accordingly.
> 
> No binary differences are present after these changes.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  include/uapi/linux/if_arp.h | 18 +++++++++---------
>  net/ipv4/arp.c              |  2 +-
>  2 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/include/uapi/linux/if_arp.h b/include/uapi/linux/if_arp.h
> index 4783af9fe520..cb6813f7783a 100644
> --- a/include/uapi/linux/if_arp.h
> +++ b/include/uapi/linux/if_arp.h
> @@ -115,18 +115,18 @@
>  
>  /* ARP ioctl request. */
>  struct arpreq {
> -	struct sockaddr	arp_pa;		/* protocol address		 */
> -	struct sockaddr	arp_ha;		/* hardware address		 */
> -	int		arp_flags;	/* flags			 */
> -	struct sockaddr arp_netmask;    /* netmask (only for proxy arps) */
> -	char		arp_dev[IFNAMSIZ];
> +	struct sockaddr_legacy	arp_pa;		/* protocol address		 */
> +	struct sockaddr_legacy	arp_ha;		/* hardware address		 */
> +	int			arp_flags;	/* flags			 */
> +	struct sockaddr_legacy	arp_netmask;    /* netmask (only for proxy arps) */
> +	char			arp_dev[IFNAMSIZ];
>  };
>  
>  struct arpreq_old {
> -	struct sockaddr	arp_pa;		/* protocol address		 */
> -	struct sockaddr	arp_ha;		/* hardware address		 */
> -	int		arp_flags;	/* flags			 */
> -	struct sockaddr	arp_netmask;    /* netmask (only for proxy arps) */
> +	struct sockaddr_legacy	arp_pa;		/* protocol address		 */
> +	struct sockaddr_legacy	arp_ha;		/* hardware address		 */
> +	int			arp_flags;	/* flags			 */
> +	struct sockaddr		arp_netmask;    /* netmask (only for proxy arps) */

I think we can use _legacy here too, 14 bytes are enough for ARP.

But whichever is fine to me because arpreq_old is not used in
kernel, so

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>


>  };
>  
>  /* ARP Flag values. */
> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> index 11c1519b3699..3a97efe1587b 100644
> --- a/net/ipv4/arp.c
> +++ b/net/ipv4/arp.c
> @@ -1185,7 +1185,7 @@ static int arp_req_get(struct net *net, struct arpreq *r)
>  
>  	read_lock_bh(&neigh->lock);
>  	memcpy(r->arp_ha.sa_data, neigh->ha,
> -	       min(dev->addr_len, sizeof(r->arp_ha.sa_data_min)));
> +	       min(dev->addr_len, sizeof(r->arp_ha.sa_data)));
>  	r->arp_flags = arp_state_to_flags(neigh);
>  	read_unlock_bh(&neigh->lock);
>  
> -- 
> 2.34.1