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

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

On Wed, 29 Jun 2022, Paolo Abeni wrote:

> 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.
>

There's still a call to mptcp_subflow_send_ack() in pm_netlink.c, so I'll 
leave both in protocol.h for now. Will squash patches 2 & 3 though.

--
Mat Martineau
Intel