linux-kernel - Re: [PATCH net-next] net: bpf: fix request

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Date:   Tue, 07 Jun 2022 10:18:27 +0200
From:   Antoine Tenart <atenart@...nel.org>
To:     Jon Maxwell <jmaxwell37@...il.com>, linux-kernel@...r.kernel.org
Cc:     davem@...emloft.net, cjebpub@...il.com, jmaxwell37@...il.com
Subject: Re: [PATCH net-next] net: bpf: fix request_sock leak in filter.c

Hi Jon,

This patch is targeted at the networking subsystem, as such (see the
"NETWORKING [GENERAL]" section in MAINTAINERS), you should send it to
netdev@...r.kernel.org and to the networking maintainers (David, Jakub,
Paolo & Eric).

This also fixes an issue and should be targeted at [net] instead of
[net-next]. Because of this you'll also need a Fixes: tag.

Quoting Jon Maxwell (2022-06-07 03:38:44)
> A customer reported a request_socket leak in a Calico cloud environment. We 
> found that a BPF program was doing a socket lookup with takes a refcnt on 
> the socket and that it was finding the request_socket but returning the parent 
> LISTEN socket via sk_to_full_sk() without decrementing the child request socket 
> 1st, resulting in request_sock slab object leak. This patch retains the 
> existing behaviour of returning full socks to the caller but it also decrements
> the child request_socket if one is present before doing so to prevent the leak.
> 
> Thanks to Curtis Taylor for all the help in diagnosing and testing this. And 
> thanks to Antoine Tenart for the reproducer and patch input.
> 
> Signed-off-by: Jon Maxwell <jmaxwell37@...il.com>
> Tested-by: Curtis Taylor <cjebpub@...il.com>
> Co-developed-by: Antoine Tenart <atenart@...nel.org>

You need to put my SoB here when using the above tag. You'll also need
to put your SoB at the end of all the above tags instead of the top.

> @@ -6514,13 +6514,14 @@ __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  {
>         struct sock *sk = __bpf_skc_lookup(skb, tuple, len, caller_net,
>                                            ifindex, proto, netns_id, flags);
> +       struct sock *sk1 = sk;
>  
>         if (sk) {
>                 sk = sk_to_full_sk(sk);
> -               if (!sk_fullsock(sk)) {
> -                       sock_gen_put(sk);

I'd suggest to add a comment here to explain why sock_gen_put is called
on the original sk.

> +               if (!sk_fullsock(sk1)) 
> +                       sock_gen_put(sk1);
> +               if (!sk_fullsock(sk))
>                         return NULL;
> -               }
>         }
>  
>         return sk;
> @@ -6551,13 +6552,14 @@ bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  {
>         struct sock *sk = bpf_skc_lookup(skb, tuple, len, proto, netns_id,
>                                          flags);
> +       struct sock *sk1 = sk;
>  
>         if (sk) {
>                 sk = sk_to_full_sk(sk);
> -               if (!sk_fullsock(sk)) {
> -                       sock_gen_put(sk);

Ditto.

> +               if (!sk_fullsock(sk1))
> +                       sock_gen_put(sk1);
> +               if (!sk_fullsock(sk))
>                         return NULL;
> -               }
>         }
>  
>         return sk;

Thanks!
Antoine