Messages in this thread | | | Date | Thu, 9 Feb 2023 10:31:50 +0530 | Subject | Re: [PATCH] usb: gadget: u_serial: Add null pointer check in gserial_resume | From | Prashanth K <> |
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On 09-02-23 01:51 am, Alan Stern wrote: > On Wed, Feb 08, 2023 at 09:15:54PM +0530, Prashanth K wrote: >> >> >> On 08-02-23 08:24 pm, Greg Kroah-Hartman wrote: >>> On Wed, Feb 08, 2023 at 07:24:47PM +0530, Prashanth K wrote: >>>> Consider a case where gserial_disconnect has already cleared >>>> gser->ioport. And if a wakeup interrupt triggers afterwards, >>>> gserial_resume gets called, which will lead to accessing of >>>> gserial->port and thus causing null pointer dereference.Add >>>> a null pointer check to prevent this. >>>> >>>> Fixes: aba3a8d01d62 (" usb: gadget: u_serial: add suspend resume callbacks") >>> >>> Nit, and our tools will complain, no " " before the "usb:" string here, >>> right? >>> >> Will fix it in next patch. >>> >>> >>>> Signed-off-by: Prashanth K <quic_prashk@quicinc.com> >>>> --- >>>> drivers/usb/gadget/function/u_serial.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c >>>> index 840626e..98be2b8 100644 >>>> --- a/drivers/usb/gadget/function/u_serial.c >>>> +++ b/drivers/usb/gadget/function/u_serial.c >>>> @@ -1428,6 +1428,9 @@ void gserial_resume(struct gserial *gser) >>>> struct gs_port *port = gser->ioport; >>>> unsigned long flags; >>>> + if (!port) >>>> + return; >>>> + >>> >>> What prevents port from going to NULL right after this check? >> In our case we got a null pointer de-reference while performing USB >> compliance tests, as the gser->port was null. Because in gserial_resume, >> spinlock_irq_save(&port->port_lock) accesses a null-pointer as port was >> already marked null by gserial_disconnect. >> >> And after gserial_resume acquires the spinlock, gserial_disconnect cant mark >> it null until the spinlock is released. We need to check if the port->lock >> is valid before accessing it, otherwise it can lead to the above mentioned >> scenario > > What happens if gserial_disconnect sets gser->port to NULL immediately > after your new check occurs, but before > spinlock_irq_save(&port->port_lock) gets called? > > You may need to add a static spinlock to prevent this from happening. > > Alan Stern In that case i guess we have to make port_lock a global variable and take it out of gs_port structure.
+ static DEFINE_SPINLOCK(port_lock);
struct gs_port { struct tty_port port; - spinlock_t port_lock;
This will require us to change all the spinlock(port->port_lock) used in u_serial.c, what do you suggest?
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