netdev - Re: [PATCH] net: bridge: enfore alignment for ethernet address

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Message-ID: <b25f8e1c-2a45-b522-52d0-7628586b2ef8@cumulusnetworks.com>
Date:   Thu, 25 Jun 2020 14:54:02 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Thomas Martitz <t.martitz@....de>, netdev@...r.kernel.org
Cc:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Felix Fietkau <nbd@....name>,
        stable@...r.kernel.org
Subject: Re: [PATCH] net: bridge: enfore alignment for ethernet address

On 25/06/2020 09:54, Thomas Martitz wrote:
> The eth_addr member is passed to ether_addr functions that require
> 2-byte alignment, therefore the member must be properly aligned
> to avoid unaligned accesses.
> 
> The problem is in place since the initial merge of multicast to unicast:
> commit 6db6f0eae6052b70885562e1733896647ec1d807 bridge: multicast to unicast
> 
> Fixes: 6db6f0eae605 ("bridge: multicast to unicast")
> Cc: Roopa Prabhu <roopa@...ulusnetworks.com>
> Cc: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Felix Fietkau <nbd@....name>
> Cc: stable@...r.kernel.org
> Signed-off-by: Thomas Martitz <t.martitz@....de>
> ---
>  net/bridge/br_private.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 7501be4eeba0..22cb2f1993ef 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -217,8 +217,8 @@ struct net_bridge_port_group {
>  	struct rcu_head			rcu;
>  	struct timer_list		timer;
>  	struct br_ip			addr;
> +	unsigned char			eth_addr[ETH_ALEN]; /* 2-byte aligned */
>  	unsigned char			flags;
> -	unsigned char			eth_addr[ETH_ALEN];
>  };
>  
>  struct net_bridge_mdb_entry {
> 

Hi Thomas,
To document it and guarantee that future struct changes won't break it I think
it'd be a good idea to add __aligned(2) for that member instead of the comment.

Other than that the patch looks good.

Thanks,
 Nik