netdev - Re: [net-next v2] tcp: Explicitly mark reserved field in tcp_zerocopy

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Message-ID: <20210206152828.6610da2b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 6 Feb 2021 15:28:28 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Arjun Roy <arjunroy.kdev@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, arjunroy@...gle.com,
        edumazet@...gle.com, soheil@...gle.com,
        David Ahern <dsahern@...il.com>,
        Leon Romanovsky <leon@...nel.org>
Subject: Re: [net-next v2] tcp: Explicitly mark reserved field in
 tcp_zerocopy_receive args.

On Sat,  6 Feb 2021 12:36:48 -0800 Arjun Roy wrote:
> From: Arjun Roy <arjunroy@...gle.com>
> 
> Explicitly define reserved field and require it to be 0-valued.

> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e1a17c6b473c..c8469c579ed8 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 -EINVAL;
>  		lock_sock(sk);
>  		err = tcp_zerocopy_receive(sk, &zc, &tss);
>  		release_sock(sk);

I was expecting we'd also throw in a check_zeroed_user().
Either we can check if the buffer is zeroed all the way,
or we can't and we shouldn't validate reserved either

	check_zeroed_user(optval + offsetof(reserved), 
			  len - offsetof(reserved))
?