Re: [bpf PATCH 4/6] bpf: sockmap, tcp_disconnect to listen transition

Martin KaFai Lau
2018-06-14T00:56:23Z

On Wed, Jun 13, 2018 at 10:50:14AM -0700, John Fastabend wrote:
> After adding checks to ensure TCP is in ESTABLISHED state when a
> sock is added we need to also ensure that user does not transition
> through tcp_disconnect() and back into ESTABLISHED state without
> sockmap removing the sock.
>
> To do this add unhash hook and remove sock from map there.
In bpf_tcp_init():
sk->sk_prot = &tcp_bpf_proto;

I may have missed a lock while reading sockmap.c.
Is it possible that tcp_disconnect() is being called while
the above assignment is also being done (e.g. through BPF_MAP_UPDATE_ELEM)?
The same situation go for the ESTABLISHED check.

>
> Reported-by: Eric Dumazet <edumazet@google.com>
> Fixes: 81110384441a ("bpf: sockmap, add hash map support")
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---
> kernel/bpf/sockmap.c | 67 +++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 50 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
> index 2e848cd..91c7b47 100644
> --- a/kernel/bpf/sockmap.c
> +++ b/kernel/bpf/sockmap.c
> @@ -130,6 +130,7 @@ struct smap_psock {
>
> struct proto *sk_proto;
> void (*save_close)(struct sock *sk, long timeout);
> + void (*save_unhash)(struct sock *sk);
> void (*save_data_ready)(struct sock *sk);
> void (*save_write_space)(struct sock *sk);
> };
> @@ -141,6 +142,7 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
> static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
> int offset, size_t size, int flags);
> static void bpf_tcp_close(struct sock *sk, long timeout);
> +static void bpf_tcp_unhash(struct sock *sk);
>
> static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
> {
> @@ -182,6 +184,7 @@ static void build_protos(struct proto prot[SOCKMAP_NUM_CONFIGS],
> {
> prot[SOCKMAP_BASE] = *base;
> prot[SOCKMAP_BASE].close = bpf_tcp_close;
> + prot[SOCKMAP_BASE].unhash = bpf_tcp_unhash;
> prot[SOCKMAP_BASE].recvmsg = bpf_tcp_recvmsg;
> prot[SOCKMAP_BASE].stream_memory_read = bpf_tcp_stream_read;
>
> @@ -215,6 +218,7 @@ static int bpf_tcp_init(struct sock *sk)
> }
>
> psock->save_close = sk->sk_prot->close;
> + psock->save_unhash = sk->sk_prot->unhash;
> psock->sk_proto = sk->sk_prot;
>
> /* Build IPv6 sockmap whenever the address of tcpv6_prot changes */
> @@ -302,28 +306,12 @@ 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;
>
> - rcu_read_lock();
> - psock = smap_psock_sk(sk);
> - if (unlikely(!psock)) {
> - rcu_read_unlock();
> - 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);
> kfree(psock->cork);
> @@ -378,6 +366,51 @@ static void bpf_tcp_close(struct sock *sk, long timeout)
> }
> 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();
> + 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.
> + */
> + 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;
> +
> + rcu_read_lock();
> + psock = smap_psock_sk(sk);
> + if (unlikely(!psock)) {
> + rcu_read_unlock();
> + 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();
> close_fun(sk, timeout);
> }
>