Re: [PATCH -resend] pps: do not crash when failed to register

[Rodolfo Giometti]

On 07/14/16 13:52, Jiri Slaby wrote:
> With this command sequence:
>   modprobe plip
>   modprobe pps_parport
>   rmmod pps_parport
> the partport_pps modules causes this crash:
>
> ===
>
> BUG: unable to handle kernel NULL pointer dereference at           (null)
> IP: [<ffffffffa110301d>] parport_detach+0x1d/0x60 [pps_parport]
> Oops: 0000 [#1] SMP
> ...
> Call Trace:
>   [<ffffffffa036a185>] parport_unregister_driver+0x65/0xc0 [parport]
>   [<ffffffff810ff667>] SyS_delete_module+0x187/0x210
>
> ===
>
> 1) plip is loaded and takes the parport device for exclusive use:
>    plip0: Parallel port at 0x378, using IRQ 7.
>
> 2) pps_parport then fails to grab the device:
>    pps_parport: parallel port PPS client
>    parport0: cannot grant exclusive access for device pps_parport
>    pps_parport: couldn't register with parport0
>
> 3) rmmod of pps_parport is then killed because it tries to access
>     pardev->name, but pardev (taken from port->cad) is NULL.
>
> So add a check for NULL in the test there too.
>
> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
> Cc: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
> ---
>   drivers/pps/clients/pps_parport.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pps/clients/pps_parport.c b/drivers/pps/clients/pps_parport.c
> index 38a8bbe74810..83797d89c30f 100644
> --- a/drivers/pps/clients/pps_parport.c
> +++ b/drivers/pps/clients/pps_parport.c
> @@ -195,7 +195,7 @@ static void parport_detach(struct parport *port)
>   	struct pps_client_pp *device;
>
>   	/* FIXME: oooh, this is ugly! */
> -	if (strcmp(pardev->name, KBUILD_MODNAME))
> +	if (!pardev || strcmp(pardev->name, KBUILD_MODNAME))
>   		/* not our port */
>   		return;

Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>

--

HCE Engineering                      e-mail: giometti@xxxxxxxxxxxxxxxxxxx
GNU/Linux Solutions                          giometti@xxxxxxxxxxxx
Linux Device Driver                          giometti@xxxxxxxx
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
Cosino Project - the quick prototyping embedded system - www.cosino.io
Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it