Re: [RFC PATCH 2/3] ipv6: Run a reverse sk_lookup on sendmsg.

[Simon Horman <horms@kernel.org>]

On Fri, Sep 13, 2024 at 10:39:20AM +0100, Tiago Lam wrote:
> This follows the same rationale provided for the ipv4 counterpart, where
> it now runs a reverse socket lookup when source addresses and/or ports
> are changed, on sendmsg, to check whether egress traffic should be
> allowed to go through or not.
> 
> As with ipv4, the ipv6 sendmsg path is also extended here to support the
> IPV6_ORIGDSTADDR ancilliary message to be able to specify a source

Hi Tiago Lam,

Some minor nits from my side.

ancilliary -> ancillary

Likewise in patch 3/3.
Flagged by checkpatch.pl --codespell

> address/port.
> 
> Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Tiago Lam <tiagolam@cloudflare.com>
> ---
>  net/ipv6/datagram.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  net/ipv6/udp.c      |  8 ++++--
>  2 files changed, 82 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
> index fff78496803d..4214dda1c320 100644
> --- a/net/ipv6/datagram.c
> +++ b/net/ipv6/datagram.c
> @@ -756,6 +756,27 @@ void ip6_datagram_recv_ctl(struct sock *sk, struct msghdr *msg,
>  }
>  EXPORT_SYMBOL_GPL(ip6_datagram_recv_ctl);
>  
> +static inline bool reverse_sk_lookup(struct flowi6 *fl6, struct sock *sk,
> +				     struct in6_addr *saddr, __be16 sport)
> +{
> +	if (static_branch_unlikely(&bpf_sk_lookup_enabled) &&
> +	    (saddr && sport) &&
> +	    (ipv6_addr_cmp(&sk->sk_v6_rcv_saddr, saddr) || inet_sk(sk)->inet_sport != sport)) {

Please consider, where it can trivially be achieved, limiting Networking
code to 80 columns wide.

Checkpatch can be run with a flag to check for this.

> +		struct sock *sk_egress;
> +
> +		bpf_sk_lookup_run_v6(sock_net(sk), IPPROTO_UDP, &fl6->daddr, fl6->fl6_dport,
> +				     saddr, ntohs(sport), 0, &sk_egress);
> +		if (!IS_ERR_OR_NULL(sk_egress) &&
> +		    atomic64_read(&sk_egress->sk_cookie) == atomic64_read(&sk->sk_cookie))
> +			return true;
> +
> +		net_info_ratelimited("No reverse socket lookup match for local addr %pI6:%d remote addr %pI6:%d\n",
> +				     &saddr, ntohs(sport), &fl6->daddr, ntohs(fl6->fl6_dport));
> +	}
> +
> +	return false;
> +}
> +
>  int ip6_datagram_send_ctl(struct net *net, struct sock *sk,
>  			  struct msghdr *msg, struct flowi6 *fl6,
>  			  struct ipcm6_cookie *ipc6)

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