netdev - RE: [Patch bpf] udp: validate checksum in udp_read

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Date:   Mon, 11 Oct 2021 22:06:01 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: RE: [Patch bpf] udp: validate checksum in udp_read_sock()

Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> It turns out the skb's in sock receive queue could have
> bad checksums, as both ->poll() and ->recvmsg() validate
> checksums. We have to do the same for ->read_sock() path
> too before they are redirected in sockmap.
> 
> Fixes: d7f571188ecf ("udp: Implement ->read_sock() for sockmap")
> Reported-by: Daniel Borkmann <daniel@...earbox.net>
> Reported-by: John Fastabend <john.fastabend@...il.com>
> Cc: Lorenz Bauer <lmb@...udflare.com>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
>  net/ipv4/udp.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 8536b2a7210b..0ae8ab5e05b4 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1808,6 +1808,17 @@ int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
>  		skb = skb_recv_udp(sk, 0, 1, &err);
>  		if (!skb)
>  			return err;
> +
> +		if (udp_lib_checksum_complete(skb)) {
> +			__UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
> +					IS_UDPLITE(sk));
> +			__UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
> +					IS_UDPLITE(sk));
> +			atomic_inc(&sk->sk_drops);
> +			kfree_skb(skb);

We could use sock_drop() here? Otherwise looks good thanks.

> +			continue;
> +		}
> +
>  		used = recv_actor(desc, skb, 0, skb->len);
>  		if (used <= 0) {
>  			if (!copied)
> -- 
> 2.30.2
>