Re: [PATCH net v2] Fix race for duplicate reqsk on identical SYN

[Eric Dumazet <edumazet@google.com>]

On Sat, Jun 15, 2024 at 12:24 AM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
>
> From: luoxuanqiang <luoxuanqiang@kylinos.cn>
> Date: Fri, 14 Jun 2024 20:42:07 +0800
> > 在 2024/6/14 18:54, Florian Westphal 写道:
> > > luoxuanqiang <luoxuanqiang@kylinos.cn> wrote:
> > >>   include/net/inet_connection_sock.h |  2 +-
> > >>   net/dccp/ipv4.c                    |  2 +-
> > >>   net/dccp/ipv6.c                    |  2 +-
> > >>   net/ipv4/inet_connection_sock.c    | 15 +++++++++++----
> > >>   net/ipv4/tcp_input.c               | 11 ++++++++++-
> > >>   5 files changed, 24 insertions(+), 8 deletions(-)
> > >>
> > >> diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
> > >> index 7d6b1254c92d..8773d161d184 100644
> > >> --- a/include/net/inet_connection_sock.h
> > >> +++ b/include/net/inet_connection_sock.h
> > >> @@ -264,7 +264,7 @@ struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
> > >>                                  struct request_sock *req,
> > >>                                  struct sock *child);
> > >>   void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
> > >> -                             unsigned long timeout);
> > >> +                             unsigned long timeout, bool *found_dup_sk);
> > > Nit:
> > >
> > > I think it would be preferrable to change retval to bool rather than
> > > bool *found_dup_sk extra arg, so one can do
>
> +1
>
>
> > >
> > > bool inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
> > >                                unsigned long timeout)
> > > {
> > >     if (!reqsk_queue_hash_req(req, timeout))
> > >             return false;
> > >
> > > i.e. let retval indicate wheter reqsk was inserted or not.
> > >
> > > Patch looks good to me otherwise.
> >
> > Thank you for your confirmation!
> >
> > Regarding your suggestion, I had considered it before,
> > but besides tcp_conn_request() calling inet_csk_reqsk_queue_hash_add(),
> > dccp_v4(v6)_conn_request() also calls it. However, there is no
> > consideration for a failed insertion within that function, so it's
> > reasonable to let the caller decide whether to check for duplicate
> > reqsk.
>
> I guess you followed 01770a1661657 where found_dup_sk was introduced,
> but note that the commit is specific to TCP SYN Cookie and TCP Fast Open
> and DCCP is not related.
>
> Then, own_req is common to TCP and DCCP, so found_dup_sk was added as an
> additional argument.
>
> However, another similar commit 5e0724d027f05 actually added own_req check
> in DCCP path.
>
> I personally would'nt care if DCCP was not changed to handle such a
> failure because DCCP will be removed next year, but I still prefer
> Florian's suggestion.
>

Other things to consider :

- I presume this patch targets net tree, and luoxuanqiang needs the
fix to reach stable trees.

- This means a Fixes: tag is needed

- This also means that we should favor a patch with no or trivial
conflicts for stable backports.

Should the patch target the net-next tree, then the requirements can
be different.