[bpf,2/5] tcp, ulp: fix leftover icsk_ulp_ops preventing sock from reattach

I found that in BPF sockmap programs once we either delete a socket
from the map or we updated a map slot and the old socket was purged
from the map that these socket can never get reattached into a map
even though their related psock has been dropped entirely at that
point.

Reason is that tcp_cleanup_ulp() leaves the old icsk->icsk_ulp_ops
intact, so that on the next tcp_set_ulp_id() the kernel returns an
-EEXIST thinking there is still some active ULP attached.

BPF sockmap is the only one that has this issue as the other user,
kTLS, only calls tcp_cleanup_ulp() from tcp_v4_destroy_sock() whereas
sockmap semantics allow dropping the socket from the map with all
related psock state being cleaned up.

Fixes: 1aa12bdf1bfb ("bpf: sockmap, add sock close() hook to remove socks")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
---
 net/ipv4/tcp_ulp.c | 2 ++
 1 file changed, 2 insertions(+)

On Thu, Aug 16, 2018 at 12:49 PM, Daniel Borkmann <daniel@iogearbox.net> wrote:
> I found that in BPF sockmap programs once we either delete a socket
> from the map or we updated a map slot and the old socket was purged
> from the map that these socket can never get reattached into a map
> even though their related psock has been dropped entirely at that
> point.
>
> Reason is that tcp_cleanup_ulp() leaves the old icsk->icsk_ulp_ops
> intact, so that on the next tcp_set_ulp_id() the kernel returns an
> -EEXIST thinking there is still some active ULP attached.
>
> BPF sockmap is the only one that has this issue as the other user,
> kTLS, only calls tcp_cleanup_ulp() from tcp_v4_destroy_sock() whereas
> sockmap semantics allow dropping the socket from the map with all
> related psock state being cleaned up.
>
> Fixes: 1aa12bdf1bfb ("bpf: sockmap, add sock close() hook to remove socks")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: John Fastabend <john.fastabend@gmail.com>

Acked-by: Song Liu <songliubraving@fb.com>

> ---
>  net/ipv4/tcp_ulp.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/tcp_ulp.c b/net/ipv4/tcp_ulp.c
> index 7dd44b6..a5995bb 100644
> --- a/net/ipv4/tcp_ulp.c
> +++ b/net/ipv4/tcp_ulp.c
> @@ -129,6 +129,8 @@ void tcp_cleanup_ulp(struct sock *sk)
>         if (icsk->icsk_ulp_ops->release)
>                 icsk->icsk_ulp_ops->release(sk);
>         module_put(icsk->icsk_ulp_ops->owner);
> +
> +       icsk->icsk_ulp_ops = NULL;
>  }
>
>  /* Change upper layer protocol for socket */
> --
> 2.9.5
>