[PATCH 3.16 108/346] pps: do not crash when failed to register

From: Ben Hutchings
Date: Sun Nov 13 2016 - 22:12:55 EST


3.16.39-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Jiri Slaby <jslaby@xxxxxxx>

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.

Link: http://lkml.kernel.org/r/20160714115245.12651-1-jslaby@xxxxxxx
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/pps/clients/pps_parport.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/pps/clients/pps_parport.c
+++ b/drivers/pps/clients/pps_parport.c
@@ -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;