netdev - Re: [net] tcp: Explicitly mark reserved field in tcp_zerocopy

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Date:   Fri, 5 Feb 2021 23:57:25 -0700
From:   David Ahern <dsahern@...il.com>
To:     Arjun Roy <arjunroy.kdev@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org
Cc:     arjunroy@...gle.com, edumazet@...gle.com, soheil@...gle.com,
        Leon Romanovsky <leon@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [net] tcp: Explicitly mark reserved field in tcp_zerocopy_receive
 args.

On 2/5/21 4:01 PM, Arjun Roy wrote:
> From: Arjun Roy <arjunroy@...gle.com>
> 
> Explicitly define reserved field and require it to be 0-valued.
> 
> Fixes: 7eeba1706eba ("tcp: Add receive timestamp support for receive zerocopy.")
> Signed-off-by: Arjun Roy <arjunroy@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Suggested-by: David Ahern <dsahern@...il.com>
> Suggested-by: Leon Romanovsky <leon@...nel.org>
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> ---
>  include/uapi/linux/tcp.h | 2 +-
>  net/ipv4/tcp.c           | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index 42fc5a640df4..8fc09e8638b3 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -357,6 +357,6 @@ struct tcp_zerocopy_receive {
>  	__u64 msg_control; /* ancillary data */
>  	__u64 msg_controllen;
>  	__u32 msg_flags;
> -	/* __u32 hole;  Next we must add >1 u32 otherwise length checks fail. */
> +	__u32 reserved; /* set to 0 for now */
>  };
>  #endif /* _UAPI_LINUX_TCP_H */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e1a17c6b473c..97aee57ab9b4 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4159,6 +4159,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
>  		}
>  		if (copy_from_user(&zc, optval, len))
>  			return -EFAULT;
> +		if (zc.reserved)
> +			return -EOPNOTSUPP;

usually invalid values for uapi return -EINVAL