Re: [PATCH v2 net-next] tcp: Warn if sock_owned_by_user() is true in tcp_child_process().

[Kuniyuki Iwashima <kuniyu@amazon.co.jp>]

From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 9 Dec 2021 00:00:35 -0800
> On Wed, Dec 8, 2021 at 5:33 PM Kuniyuki Iwashima <kuniyu@amazon.co.jp> wrote:
>>
>> While creating a child socket from ACK (not TCP Fast Open case), before
>> v2.3.41, we used to call bh_lock_sock() later than now; it was called just
>> before tcp_rcv_state_process().  The full socket was put into an accept
>> queue and exposed to other CPUs before bh_lock_sock() so that process
>> context might have acquired the lock by then.  Thus, we had to check if any
>> process context was accessing the socket before tcp_rcv_state_process().
>>
> 
> I think you misunderstood me.
> 
> I think this code is not dead yet, so I would :
> 
> Not include a Fixes: tag to avoid unnecessary backports (of a patch
> and its revert)
> 
> If you want to get syzbot coverage for few releases, especially with
> MPTCP and synflood,
> you  can then submit a patch like the following.

Sorry, I got on the same page.
Let me take a look at MPTCP, then if I still think it is dead code, I will
submit the patch.

Thank you.


> 
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index cf913a66df17..19da6e442fca 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -843,6 +843,9 @@ int tcp_child_process(struct sock *parent, struct
> sock *child,
>                  * in main socket hash table and lock on listening
>                  * socket does not protect us more.
>                  */
> +
> +               /* Check if this code path is obsolete ? */
> +               WARN_ON_ONCE(1);
>                 __sk_add_backlog(child, skb);
>         }