Re: Possible race in nsc-ircc.ko

On Fri, Aug 25, 2017 at 05:05:25PM +0300, Anton Volkov wrote:

Hello.

While searching for races in the Linux kernel I've come across
"drivers/net/irda/nsc-ircc.ko" module. Here is a question that I came up
with while analyzing results. Lines are given using the info from Linux
v4.12.

Consider the following case:

Thread 1:                   Thread 2:
nsc_ircc_init
->nsc_ircc_open
    self = netdev_priv(dev)
    register_netdev(dev)
                            nsc_ircc_net_ioctl
                            ->nsc_ircc_change_speed
    self->dongle_id = ...       <READ self->io.dongle_id>
    (nsc-ircc.c: line 485)      (nsc-ircc.c: line 1318)
    platform_device_register_simple

Before the initialization of self->dongle_id in msc_ircc_open() its value is
0. Thus if read access to its value in nsc_ircc_change_speed occurs before
the initialization there will be an attempt to change speed of dongle with
undesired id (if the dongle with id 0 exists). Is this case feasible from
your point of view?

Thank you for your time.

-- Anton Volkov

	A first glance, that seems like a valid race. I'm not sure if
there is a netdev lock/status to protect the driver, because it looks
like doing any operation on a device before "open" has completed would
be dangerous for most drivers.
	I don't have time to check the code paths, as I have not
looked at that code in ages.
	Good luck !

	Jean