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

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Message-ID: <lsq.1479082460.318193638@decadent.org.uk>
Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Rodolfo Giometti" <giometti@...eenne.com>,
        "Jiri Slaby" <jslaby@...e.cz>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 108/346] pps: do not crash when failed to register

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

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

From: Jiri Slaby <jslaby@...e.cz>

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@suse.cz
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Acked-by: Rodolfo Giometti <giometti@...eenne.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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;