linux-kernel - [PATCH] media: saa7134: Fix a NULL pointer dereference in saa7134

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Date:   Tue, 25 Jan 2022 01:19:30 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Tasos Sahanidis <tasos@...ossah.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] media: saa7134: Fix a NULL pointer dereference in saa7134_initdev()

In saa7134_initdev(), the return value of vdev_init() is assigned to
dev->video_dev and there is a dereference of it after that. The return
value of vdev_init() will be NULL on the failure allocation, which could
lead to 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: a9622391acb ("V4L/DVB (6792): Fix VBI support")
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/saa7134/saa7134-core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/media/pci/saa7134/saa7134-core.c b/drivers/media/pci/saa7134/saa7134-core.c
index 96328b0af164..0de0b00540b6 100644
--- a/drivers/media/pci/saa7134/saa7134-core.c
+++ b/drivers/media/pci/saa7134/saa7134-core.c
@@ -1202,6 +1202,11 @@ static int saa7134_initdev(struct pci_dev *pci_dev,
 		pr_info("%s: Overlay support disabled.\n", dev->name);
 
 	dev->video_dev = vdev_init(dev,&saa7134_video_template,"video");
+	if (!dev->video_dev) {
+		err = -ENOMEM;
+		goto err_unregister_video;
+	}
+
 	dev->video_dev->ctrl_handler = &dev->ctrl_handler;
 	dev->video_dev->lock = &dev->lock;
 	dev->video_dev->queue = &dev->video_vbq;
@@ -1224,6 +1229,11 @@ static int saa7134_initdev(struct pci_dev *pci_dev,
 	       dev->name, video_device_node_name(dev->video_dev));
 
 	dev->vbi_dev = vdev_init(dev, &saa7134_video_template, "vbi");
+	if (!dev->vbi_dev) {
+		err = -ENOMEM;
+		goto err_unregister_video;
+	}
+
 	dev->vbi_dev->ctrl_handler = &dev->ctrl_handler;
 	dev->vbi_dev->lock = &dev->lock;
 	dev->vbi_dev->queue = &dev->vbi_vbq;
-- 
2.25.1