netdev - Re: [PATCH bpf-next v4 1/2] bpf: setup socket family and addresses in bpf_prog_test_run

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Message-ID: <6d96e856-c47f-bdfc-8a6d-8836577e6200@gmail.com>
Date:   Sun, 2 Aug 2020 13:19:00 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dmitry Yakunin <zeil@...dex-team.ru>, alexei.starovoitov@...il.com,
        daniel@...earbox.net, netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     sdf@...gle.com
Subject: Re: [PATCH bpf-next v4 1/2] bpf: setup socket family and addresses in
 bpf_prog_test_run_skb



On 8/2/20 11:26 AM, Dmitry Yakunin wrote:
> Now it's impossible to test all branches of cgroup_skb bpf program which
> accesses skb->family and skb->{local,remote}_ip{4,6} fields because they
> are zeroed during socket allocation. This commit fills socket family and
> addresses from related fields in constructed skb.
> 
> v2:
>   - fix build without CONFIG_IPV6 (kernel test robot <lkp@...el.com>)
> 
> Signed-off-by: Dmitry Yakunin <zeil@...dex-team.ru>
> ---
>  net/bpf/test_run.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index b03c469..2521b27 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -449,6 +449,23 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  	skb->protocol = eth_type_trans(skb, current->nsproxy->net_ns->loopback_dev);
>  	skb_reset_network_header(skb);
>  

At this point, there is no guarantee the skb contains these headers.

You will have to add safety checks against skb->len

> +	switch (skb->protocol) {
> +	case htons(ETH_P_IP):
> +		sk->sk_family = AF_INET;
> +		sk->sk_rcv_saddr = ip_hdr(skb)->saddr;
> +		sk->sk_daddr = ip_hdr(skb)->daddr;
> +		break;
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case htons(ETH_P_IPV6):
> +		sk->sk_family = AF_INET6;
> +		sk->sk_v6_rcv_saddr = ipv6_hdr(skb)->saddr;
> +		sk->sk_v6_daddr = ipv6_hdr(skb)->daddr;
> +		break;
> +#endif
> +	default:
> +		break;
> +	}
> +
>  	if (is_l2)
>  		__skb_push(skb, hh_len);
>  	if (is_direct_pkt_access)
>