linux-kernel - [PATCH] media: pci: cx23855-video.c: Fix a NULL pointer dereference in cx23885_video

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Date:   Tue, 25 Jan 2022 01:16:18 +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: pci: cx23855-video.c: Fix a NULL pointer dereference in cx23885_video_register()

In cx23885_video_register(), the return value of cx23885_vdev_init() is
assigned to dev->video_dev and there is a dereference of it after that.
the return value of cx23885_vdev_init() could be NULL on failure of
allocation, which could lead to a NULL pointer dereference.

the same as dev->vbi_dev.

Fix this bug by adding a NULL check of dev->video_dev and dev->vbi_dev.

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-video.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/media/pci/cx23885/cx23885-video.c b/drivers/media/pci/cx23885/cx23885-video.c
index a380e0920a21..1b95109eff8c 100644
--- a/drivers/media/pci/cx23885/cx23885-video.c
+++ b/drivers/media/pci/cx23885/cx23885-video.c
@@ -1353,6 +1353,11 @@ int cx23885_video_register(struct cx23885_dev *dev)
 	/* register Video device */
 	dev->video_dev = cx23885_vdev_init(dev, dev->pci,
 		&cx23885_video_template, "video");
+	if (!dev->video_dev) {
+		err = -ENOMEM;
+		goto fail_unreg;
+	}
+
 	dev->video_dev->queue = &dev->vb2_vidq;
 	dev->video_dev->device_caps = V4L2_CAP_READWRITE | V4L2_CAP_STREAMING |
 				      V4L2_CAP_AUDIO | V4L2_CAP_VIDEO_CAPTURE;
@@ -1381,6 +1386,11 @@ int cx23885_video_register(struct cx23885_dev *dev)
 	/* register VBI device */
 	dev->vbi_dev = cx23885_vdev_init(dev, dev->pci,
 		&cx23885_vbi_template, "vbi");
+	if (!dev->vbi_dev) {
+		err = -ENOMEM;
+		goto fail_unreg;
+	}
+
 	dev->vbi_dev->queue = &dev->vb2_vbiq;
 	dev->vbi_dev->device_caps = V4L2_CAP_READWRITE | V4L2_CAP_STREAMING |
 				    V4L2_CAP_AUDIO | V4L2_CAP_VBI_CAPTURE;
-- 
2.25.1