netdev - Re: [PATCH v3 net-next 1/5] net: add TIME_WAIT logic to sk_to_full

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Message-ID: <CANn89iLv=7fqrYLEF-hO1_EOK4xVEHmD60bqeiJ5Kydc3bJ0+A@mail.gmail.com>
Date: Mon, 14 Oct 2024 16:27:50 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Brian Vazquez <brianvv@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Martin KaFai Lau <martin.lau@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Neal Cardwell <ncardwell@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH v3 net-next 1/5] net: add TIME_WAIT logic to sk_to_full_sk()

On Mon, Oct 14, 2024 at 4:01 PM Brian Vazquez <brianvv@...gle.com> wrote:
>
> Thanks Eric for the patch series!  I left some comments inline
>
>
> On Thu, Oct 10, 2024 at 1:48 PM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > TCP will soon attach TIME_WAIT sockets to some ACK and RST.
> >
> > Make sure sk_to_full_sk() detects this and does not return
> > a non full socket.
> >
> > v3: also changed sk_const_to_full_sk()
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > ---
> >  include/linux/bpf-cgroup.h | 2 +-
> >  include/net/inet_sock.h    | 8 ++++++--
> >  net/core/filter.c          | 6 +-----
> >  3 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> > index ce91d9b2acb9f8991150ceead4475b130bead438..f0f219271daf4afea2666c4d09fd4d1a8091f844 100644
> > --- a/include/linux/bpf-cgroup.h
> > +++ b/include/linux/bpf-cgroup.h
> > @@ -209,7 +209,7 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
> >         int __ret = 0;                                                         \
> >         if (cgroup_bpf_enabled(CGROUP_INET_EGRESS) && sk) {                    \
> >                 typeof(sk) __sk = sk_to_full_sk(sk);                           \
> > -               if (sk_fullsock(__sk) && __sk == skb_to_full_sk(skb) &&        \
> > +               if (__sk && __sk == skb_to_full_sk(skb) &&             \
> >                     cgroup_bpf_sock_enabled(__sk, CGROUP_INET_EGRESS))         \
> >                         __ret = __cgroup_bpf_run_filter_skb(__sk, skb,         \
> >                                                       CGROUP_INET_EGRESS); \
> > diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
> > index f01dd273bea69d2eaf7a1d28274d7f980942b78a..56d8bc5593d3dfffd5f94cf7c6383948881917df 100644
> > --- a/include/net/inet_sock.h
> > +++ b/include/net/inet_sock.h
> > @@ -321,8 +321,10 @@ static inline unsigned long inet_cmsg_flags(const struct inet_sock *inet)
> >  static inline struct sock *sk_to_full_sk(struct sock *sk)
> >  {
> >  #ifdef CONFIG_INET
> > -       if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
> > +       if (sk && READ_ONCE(sk->sk_state) == TCP_NEW_SYN_RECV)
> >                 sk = inet_reqsk(sk)->rsk_listener;
> > +       if (sk && READ_ONCE(sk->sk_state) == TCP_TIME_WAIT)
> > +               sk = NULL;
> >  #endif
> >         return sk;
> >  }
> > @@ -331,8 +333,10 @@ static inline struct sock *sk_to_full_sk(struct sock *sk)
> >  static inline const struct sock *sk_const_to_full_sk(const struct sock *sk)
> >  {
> >  #ifdef CONFIG_INET
> > -       if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
> > +       if (sk && READ_ONCE(sk->sk_state) == TCP_NEW_SYN_RECV)
> >                 sk = ((const struct request_sock *)sk)->rsk_listener;
> > +       if (sk && READ_ONCE(sk->sk_state) == TCP_TIME_WAIT)
> > +               sk = NULL;
> >  #endif
> >         return sk;
> >  }
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index bd0d08bf76bb8de39ca2ca89cda99a97c9b0a034..202c1d386e19599e9fc6e0a0d4a95986ba6d0ea8 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -6778,8 +6778,6 @@ __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
> >                 /* sk_to_full_sk() may return (sk)->rsk_listener, so make sure the original sk
> >                  * sock refcnt is decremented to prevent a request_sock leak.
> >                  */
> > -               if (!sk_fullsock(sk2))
> > -                       sk2 = NULL;
>
> IIUC, we still want the condition above since sk_to_full_sk can return
> the request socket in which case the helper should return NULL, so we
> still need the refcnt decrement?
>
> >                 if (sk2 != sk) {
> >                         sock_gen_put(sk);

Note that we call sock_gen_put(sk) here, not sock_gen_put(sk2);

sk is not NULL here, so if sk2 is NULL, we will take this branch.

> >                         /* Ensure there is no need to bump sk2 refcnt */
> > @@ -6826,8 +6824,6 @@ bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
> >                 /* sk_to_full_sk() may return (sk)->rsk_listener, so make sure the original sk
> >                  * sock refcnt is decremented to prevent a request_sock leak.
> >                  */
> > -               if (!sk_fullsock(sk2))
> > -                       sk2 = NULL;
>
> Same as above.

Should be fine I think.