Patch "pps: do not crash when failed to register" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

pps: do not crash when failed to register

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
pps-do-not-crash-when-failed-to-register.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Slaby <[email protected]>
Date: Wed, 20 Jul 2016 15:45:08 -0700
Subject: pps: do not crash when failed to register

From: Jiri Slaby <[email protected]>

commit 368301f2fe4b07e5fb71dba3cc566bc59eb6705f upstream.

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: parport_detach+0x1d/0x60 [pps_parport]
  Oops: 0000 [#1] SMP
  ...
  Call Trace:
    parport_unregister_driver+0x65/0xc0 [parport]
    SyS_delete_module+0x187/0x210

The sequence that builds up to this is:

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.

---
 drivers/pps/clients/pps_parport.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -195,7 +195,7 @@ static void parport_detach(struct parpor
 	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;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/pps-do-not-crash-when-failed-to-register.patch