linux-kernel - re: media: rcar-vin: add group allocator functions

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Message-ID: <12ca5ca8-a582-5899-6dd5-c064e4b54e2b@canonical.com>
Date:   Tue, 24 Apr 2018 14:14:02 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: media: rcar-vin: add group allocator functions

Hi there,

While running static analysis on linux-next today a null pointer
dereference issue was detected by CoverityScan. The following commit
introduced the issue:

commit 3bb4c3bc85bf77a76c921671800bde2e1bf82a88
Author: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
Date:   Sat Apr 14 07:57:18 2018 -0400

    media: rcar-vin: add group allocator functions

The analysis is as follows:

339 static void rvin_group_put(struct rvin_dev *vin)
340 {
341        mutex_lock(&vin->group->lock);
342
   1. assign_zero: Assigning: vin->group = NULL.

343        vin->group = NULL;
344        vin->v4l2_dev.mdev = NULL;
345
    CID 1468359 (#1 of 1): Explicit null dereferenced (FORWARD_NULL)
    2. var_deref_op: Dereferencing null pointer vin->group.

346        if (WARN_ON(vin->group->vin[vin->id] != vin))
347                goto out;
348

vin->group is NULL however the WARN_ON is dereferencing it, causing an
OOPS.  I don't know how this should be fixed, hence I am sending this
bug report.

Regards,

Colin