Re: [PATCH mptcp-net 3/3] mptcp: Acquire the subflow socket lock before modifying MP_PRIO flags

[Paolo Abeni <pabeni@redhat.com>]

On Tue, 2022-06-28 at 12:03 -0700, Mat Martineau wrote:
> When setting up a subflow's flags for sending MP_PRIO MPTCP options, the
> subflow socket lock was not held while reading and modifying several
> struct members that are also read and modified in mptcp_write_options().
> 
> Acquire the subflow socket lock earlier and send the MP_PRIO ACK with
> that lock already acquired.
> 
> Fixes: 067065422fcd ("mptcp: add the outgoing MP_PRIO support")
> Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
> ---
>  net/mptcp/pm_netlink.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
> index d04b34fc9a8e..05c6a95e9c28 100644
> --- a/net/mptcp/pm_netlink.c
> +++ b/net/mptcp/pm_netlink.c
> @@ -729,11 +729,13 @@ static int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
>  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
>  		struct sock *sk = (struct sock *)msk;
>  		struct mptcp_addr_info local;
> +		bool slow;
>  
>  		local_address((struct sock_common *)ssk, &local);
>  		if (!mptcp_addresses_equal(&local, addr, addr->port))
>  			continue;
>  
> +		slow = lock_sock_fast(ssk);
>  		if (subflow->backup != bkup)
>  			msk->last_snd = NULL;
>  		subflow->backup = bkup;
> @@ -742,7 +744,8 @@ static int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
>  		__MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIOTX);
>  
>  		pr_debug("send ack for mp_prio");
> -		mptcp_subflow_send_ack(ssk);
> +		__mptcp_subflow_send_ack(ssk);
> +		unlock_sock_fast(ssk, slow);

After this chunk, we can remove mptcp_subflow_send_ack() from
protocol.h and make it static. I think it's easier squashing this patch
into the previous one.

Thanks!

Paolo
>  
>  		return 0;
>  	}