Re: [PATCH net-next] mptcp: fix infinite loop on recvmsg()/worker() race.

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

On Tue, 6 Oct 2020, Paolo Abeni wrote:

> If recvmsg() and the workqueue race to dequeue the data
> pending on some subflow, the current mapping for such
> subflow covers several skbs and some of them have not
> reached yet the received, either the worker or recvmsg()
> can find a subflow with the data_avail flag set - since
> the current mapping is valid and in sequence - but no
> skbs in the receive queue - since the other entity just
> processed them.
>
> The above will lead to an unbounded loop in __mptcp_move_skbs()
> and a subsequent hang of any task trying to acquiring the msk
> socket lock.
>
> This change addresses the issue stopping the __mptcp_move_skbs()
> loop as soon as we detect the above race (empty receive queue
> with data_avail set).
>
> Reported-and-tested-by: syzbot+fcf8ca5817d6e92c6567@syzkaller.appspotmail.com
> Fixes: ab174ad8ef76 ("mptcp: move ooo skbs into msk out of order queue.")
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> net/mptcp/protocol.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel