[PATCH v2] tty/serial: atmel: use port->name as name in request_irq()

[Rob Herring]

On Fri, May 4, 2018 at 5:28 AM, Richard Genoud <richard.genoud at gmail.com> wrote:
> On 04/05/2018 10:14, Sebastian Andrzej Siewior wrote:
>> I was puzzled while looking at /proc/interrupts and random things showed
>> up between reboots. This occurred more often but I realised it later. The
>> "correct" output should be:
>> |38:      11861  atmel-aic5   2 Level     ttyS0
>>
>> but I saw sometimes
>> |38:       6426  atmel-aic5   2 Level     tty1
>>
>> and accounted it wrongly as correct. This is use after free and the
>> former example randomly got the "old" pointer which pointed to the same
>> content. With SLAB_FREELIST_RANDOM and HARDENED I even got
>> |38:       7067  atmel-aic5   2 Level     E=Started User Manager for UID 0
>>
>> or other nonsense.
>> As it turns out the tty, pointer that is accessed in atmel_startup(), is
>> freed() before atmel_shutdown(). It seems to happen quite often that the
>> tty for ttyS0 is allocated and freed while ->shutdown is not invoked. I
>> don't do anything special - just a systemd boot :)
>>
>> Use port->name as the IRQ name for request_irq(). This exists as long as
>> the driver is loaded so no use-after-free here.
>> For backports before v4.12 I suggest to use `"atmel_serial"' instead
>> `port->name' (that member was introduced in f7048b15900f ("tty: serial_core:
>> Add name field to uart_port struct").
>>
>> Cc: stable at vger.kernel.org
> I think it's safer to use:
> Cc: stable at vger.kernel.org # 4.14
> Because the stable team may miss your comment, and even if they don't, I
> think it's not their role to adapt the patch to 4.9.x (and test it !)
> IMHO, the best way is to add # 4.14 and when it's applied on 4.14.x,
> send a tested backport for 4.9.x
>
> Besides that, you can add my:
> Acked-by: Richard Genoud <richard.genoud at gmail.com>
>
> Rob, do you agree with this fix ?

Yes, one less dependency on tty struct in serial drivers is a good
thing. However, I find port->name to be a somewhat pointless addition.
Most platform drivers (which most serial drivers are) use the device
name for registering their IRQ. And now serial drivers may not even
have a tty with serdev. Using the device name would also solve your
backporting issue. But either way:

Acked-by: Rob Herring <robh at kernel.org>

Rob