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Message-ID: <CAH3MdRU-0p9wno4Vmo6xCaEF9r83+WP_UBLccqA0tmcP3yOCnA@mail.gmail.com>
Date: Mon, 17 Sep 2018 14:09:02 -0700
From: Y Song <ys114321@...il.com>
To: John Fastabend <john.fastabend@...il.com>
Cc: edumazet@...gle.com, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
netdev <netdev@...r.kernel.org>
Subject: Re: [bpf PATCH 2/3] bpf: sockmap, fix transition through disconnect
without close
On Mon, Sep 17, 2018 at 10:32 AM John Fastabend
<john.fastabend@...il.com> wrote:
>
> It is possible (via shutdown()) for TCP socks to go trough TCP_CLOSE
> state via tcp_disconnect() without actually calling tcp_close which
> would then call our bpf_tcp_close() callback. Because of this a user
> could disconnect a socket then put it in a LISTEN state which would
> break our assumptions about sockets always being ESTABLISHED state.
>
> To resolve this rely on the unhash hook, which is called in the
> disconnect case, to remove the sock from the sockmap.
>
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Fixes: 1aa12bdf1bfb ("bpf: sockmap, add sock close() hook to remove socks")
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
> kernel/bpf/sockmap.c | 71 +++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 52 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
> index 998b7bd..f6ab7f3 100644
> --- a/kernel/bpf/sockmap.c
> +++ b/kernel/bpf/sockmap.c
> @@ -132,6 +132,7 @@ struct smap_psock {
> struct work_struct gc_work;
>
> struct proto *sk_proto;
> + void (*save_unhash)(struct sock *sk);
> void (*save_close)(struct sock *sk, long timeout);
> void (*save_data_ready)(struct sock *sk);
> void (*save_write_space)(struct sock *sk);
> @@ -143,6 +144,7 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
> static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
> static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
> int offset, size_t size, int flags);
> +static void bpf_tcp_unhash(struct sock *sk);
> static void bpf_tcp_close(struct sock *sk, long timeout);
>
> static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
> @@ -184,6 +186,7 @@ static void build_protos(struct proto prot[SOCKMAP_NUM_CONFIGS],
> struct proto *base)
> {
> prot[SOCKMAP_BASE] = *base;
> + prot[SOCKMAP_BASE].unhash = bpf_tcp_unhash;
> prot[SOCKMAP_BASE].close = bpf_tcp_close;
> prot[SOCKMAP_BASE].recvmsg = bpf_tcp_recvmsg;
> prot[SOCKMAP_BASE].stream_memory_read = bpf_tcp_stream_read;
> @@ -217,6 +220,7 @@ static int bpf_tcp_init(struct sock *sk)
> return -EBUSY;
> }
>
> + psock->save_unhash = sk->sk_prot->unhash;
> psock->save_close = sk->sk_prot->close;
> psock->sk_proto = sk->sk_prot;
>
> @@ -305,30 +309,12 @@ static struct smap_psock_map_entry *psock_map_pop(struct sock *sk,
> return e;
> }
>
> -static void bpf_tcp_close(struct sock *sk, long timeout)
> +static void bpf_tcp_remove(struct sock *sk, struct smap_psock *psock)
> {
> - void (*close_fun)(struct sock *sk, long timeout);
> struct smap_psock_map_entry *e;
> struct sk_msg_buff *md, *mtmp;
> - struct smap_psock *psock;
> struct sock *osk;
>
> - lock_sock(sk);
> - rcu_read_lock();
> - psock = smap_psock_sk(sk);
> - if (unlikely(!psock)) {
> - rcu_read_unlock();
> - release_sock(sk);
> - return sk->sk_prot->close(sk, timeout);
> - }
> -
> - /* The psock may be destroyed anytime after exiting the RCU critial
> - * section so by the time we use close_fun the psock may no longer
> - * be valid. However, bpf_tcp_close is called with the sock lock
> - * held so the close hook and sk are still valid.
> - */
> - close_fun = psock->save_close;
> -
> if (psock->cork) {
> free_start_sg(psock->sock, psock->cork, true);
> kfree(psock->cork);
> @@ -379,6 +365,53 @@ static void bpf_tcp_close(struct sock *sk, long timeout)
> kfree(e);
> e = psock_map_pop(sk, psock);
> }
> +}
> +
> +static void bpf_tcp_unhash(struct sock *sk)
> +{
> + void (*unhash_fun)(struct sock *sk);
> + struct smap_psock *psock;
> +
> + rcu_read_lock();
> + psock = smap_psock_sk(sk);
> + if (unlikely(!psock)) {
> + rcu_read_unlock();
> + release_sock(sk);
Can socket be released here?
> + return sk->sk_prot->unhash(sk);
> + }
> +
> + /* The psock may be destroyed anytime after exiting the RCU critial
> + * section so by the time we use close_fun the psock may no longer
> + * be valid. However, bpf_tcp_close is called with the sock lock
> + * held so the close hook and sk are still valid.
> + */
the comments above are not correct. A copy-paste mistake?
> + unhash_fun = psock->save_unhash;
> + bpf_tcp_remove(sk, psock);
> + rcu_read_unlock();
> + unhash_fun(sk);
> +}
> +
> +static void bpf_tcp_close(struct sock *sk, long timeout)
> +{
> + void (*close_fun)(struct sock *sk, long timeout);
> + struct smap_psock *psock;
> +
> + lock_sock(sk);
> + rcu_read_lock();
> + psock = smap_psock_sk(sk);
> + if (unlikely(!psock)) {
> + rcu_read_unlock();
> + release_sock(sk);
> + return sk->sk_prot->close(sk, timeout);
> + }
> +
> + /* The psock may be destroyed anytime after exiting the RCU critial
> + * section so by the time we use close_fun the psock may no longer
> + * be valid. However, bpf_tcp_close is called with the sock lock
> + * held so the close hook and sk are still valid.
> + */
> + close_fun = psock->save_close;
> + bpf_tcp_remove(sk, psock);
> rcu_read_unlock();
> release_sock(sk);
> close_fun(sk, timeout);
>
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