linux-kernel - [PATCH] media: media/pci: Fix a NULL pointer dereference in cx23885_417

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Date:   Tue, 25 Jan 2022 01:06:10 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] media: media/pci: Fix a NULL pointer dereference in cx23885_417_register()

In cx23885_417_register(), the return value of cx23885_video_dev_alloc() 
is assigned to dev->v4l_device() and there is a dereference of it after
that. the return value of cx23885_video_dev_alloc() could be NULL on 
failure of allocation, which could lead to a NULL pointer dereference.

Fix this bug by adding a NULL check of dev->v4l_device.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 453afdd9ce33 ("[media] cx23885: convert to vb2")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
---
The analysis employs differential checking to identify inconsistent 
security operations (e.g., checks or kfrees) between two code paths 
and confirms that the inconsistent operations are not recovered in the
current function or the callers, so they constitute bugs. 

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

 drivers/media/pci/cx23885/cx23885-417.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/pci/cx23885/cx23885-417.c b/drivers/media/pci/cx23885/cx23885-417.c
index 434677bd4ad1..fcc9c1117ed1 100644
--- a/drivers/media/pci/cx23885/cx23885-417.c
+++ b/drivers/media/pci/cx23885/cx23885-417.c
@@ -1521,6 +1521,8 @@ int cx23885_417_register(struct cx23885_dev *dev)
 	/* Allocate and initialize V4L video device */
 	dev->v4l_device = cx23885_video_dev_alloc(tsport,
 		dev->pci, &cx23885_mpeg_template, "mpeg");
+	if (!dev->v4l_device)
+		return -ENOMEM;
 	q = &dev->vb2_mpegq;
 	q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 	q->io_modes = VB2_MMAP | VB2_USERPTR | VB2_DMABUF | VB2_READ;
-- 
2.25.1