[PATCH] media: saa7146: hexium_orion: Fix a NULL pointer dereference in hexium_attach()

[Zhou Qingyang]

In hexium_attach(dev, info), saa7146_vv_init() is called to allocate
a new memory for dev->vv_data. In hexium_detach(), saa7146_vv_release()
will be called and there is a dereference of dev->vv_data in
saa7146_vv_release(), which could lead to a NULL pointer dereference
on failure of saa7146_vv_init() according to the following logic.

Both hexium_attach() and hexium_detach() are callback functions of
the variable 'extension', so there exists a possible call chain directly
from hexium_attach() to hexium_detach():

hexium_attach(dev, info) -- fail to alloc memory to dev->vv_data
	|		    		in saa7146_vv_init().
	|
	|
hexium_detach() -- a dereference of dev->vv_data in saa7146_vv_release()

Fix this bug by adding a check of saa7146_vv_init().

This bug was found by a static analyzer. 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.

Builds with CONFIG_VIDEO_HEXIUM_ORION=m show no new warnings,
and our static analyzer no longer warns about this code.

Signed-off-by: Zhou Qingyang <zhou1615@xxxxxxx>
---
 drivers/media/pci/saa7146/hexium_orion.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/media/pci/saa7146/hexium_orion.c b/drivers/media/pci/saa7146/hexium_orion.c
index 39d14c179d22..2eb4bee16b71 100644
--- a/drivers/media/pci/saa7146/hexium_orion.c
+++ b/drivers/media/pci/saa7146/hexium_orion.c
@@ -355,10 +355,16 @@ static struct saa7146_ext_vv vv_data;
 static int hexium_attach(struct saa7146_dev *dev, struct saa7146_pci_extension_data *info)
 {
 	struct hexium *hexium = (struct hexium *) dev->ext_priv;
+	int ret;
 
 	DEB_EE("\n");
 
-	saa7146_vv_init(dev, &vv_data);
+	ret = saa7146_vv_init(dev, &vv_data);
+	if (ret) {
+		pr_err("Error in saa7146_vv_init()\n");
+		return ret;
+	}
+
 	vv_data.vid_ops.vidioc_enum_input = vidioc_enum_input;
 	vv_data.vid_ops.vidioc_g_input = vidioc_g_input;
 	vv_data.vid_ops.vidioc_s_input = vidioc_s_input;
-- 
2.25.1