netdev - Re: [PATCH v2 net] dccp/tcp: Unhash sk from ehash for tb2 alloc failure after check

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Date: Wed, 14 Feb 2024 10:05:33 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Joanne Koong <joannelkoong@...il.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v2 net] dccp/tcp: Unhash sk from ehash for tb2 alloc
 failure after check_estalblished().

On Tue, Feb 13, 2024 at 10:42 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> syzkaller reported a warning [0] in inet_csk_destroy_sock() with no
> repro.
>
>   WARN_ON(inet_sk(sk)->inet_num && !inet_csk(sk)->icsk_bind_hash);
>
> However, the syzkaller's log hinted that connect() failed just before
> the warning due to FAULT_INJECTION.  [1]
>
> When connect() is called for an unbound socket, we search for an
> available ephemeral port.  If a bhash bucket exists for the port, we
> call __inet_check_established() or __inet6_check_established() to check
> if the bucket is reusable.
>
> If reusable, we add the socket into ehash and set inet_sk(sk)->inet_num.
>
> Later, we look up the corresponding bhash2 bucket and try to allocate
> it if it does not exist.
>
> Although it rarely occurs in real use, if the allocation fails, we must
> revert the changes by check_established().  Otherwise, an unconnected
> socket could illegally occupy an ehash entry.
>
> Note that we do not put tw back into ehash because sk might have
> already responded to a packet for tw and it would be better to free
> tw earlier under such memory presure.
>
> [0]:
>
> Reported-by: syzkaller <syzkaller@...glegroups.com>
> Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> v2:
>   * Unhash twsk from bhash/bhash2
>
> v1: https://lore.kernel.org/netdev/20240209025409.27235-1-kuniyu@amazon.com/
> ---
>  net/ipv4/inet_hashtables.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index 93e9193df544..b22c71f93297 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -1130,10 +1130,31 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
>         return 0;
>
>  error:
> +       if (sk_hashed(sk)) {
> +               spinlock_t *lock = inet_ehash_lockp(hinfo, sk->sk_hash);
> +
> +               sock_prot_inuse_add(net, sk->sk_prot, -1);
> +
> +               spin_lock(lock);
> +               sk_nulls_del_node_init_rcu(sk);
> +               spin_unlock(lock);
> +
> +               sk->sk_hash = 0;
> +               inet_sk(sk)->inet_sport = 0;
> +               inet_sk(sk)->inet_num = 0;
> +
> +               if (tw)
> +                       inet_twsk_bind_unhash(tw, hinfo);
> +       }
> +
>         spin_unlock(&head2->lock);
>         if (tb_created)
>                 inet_bind_bucket_destroy(hinfo->bind_bucket_cachep, tb);
>         spin_unlock_bh(&head->lock);
> +
> +       if (tw)
> +               inet_twsk_deschedule_put(tw);

Please make sure to call this while BH is still disabled.


    spin_unlock(&head->lock);
    if (tw)
        inet_twsk_deschedule_put(tw);
   local_bh_enable();

Thanks.

> +
>         return -ENOMEM;
>  }
>
> --
> 2.30.2
>