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Date:   Fri, 21 Jun 2019 18:04:38 -0700
From:   Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
To:     hverkuil@xs4all.nl
Cc:     mchehab@kernel.org, linux-media@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: [Linux-kernel-mentees] [PATCH v4 RESEND] Media: Radio: Change
 devm_k*alloc to k*alloc
Message-ID: <20190622010438.GA10125@luke-XPS-13>
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Change devm_k*alloc to k*alloc to manually allocate memory 

The manual allocation and freeing of memory is necessary because when
the USB radio is disconnected, the memory associated with devm_k*alloc
is freed. Meaning if we still have unresolved references to the radio
device, then we get use-after-free errors. 

This patch fixes this by manually allocating memory, and freeing it in 
the v4l2.release callback that gets called when the last radio device
exits. 

Reported-and-tested-by: syzbot+a4387f5b6b799f6becbf@syzkaller.appspotmail.com
Signed-off-by: Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
---
Changes in RESEND: 
+ Added reported-and-tested-by tag
+ Further updated description
- Removed whitespace in patch description
Changes in v4:
- Removed whitespace to fix checkpatch.pl errors
Changes in v3:
+ Update release method in v2 for v4l2.release callback 
+ Assign v4l2.release callback to release method
- Remove vdev.release callback used in v2
Changes in v2:
+ Create raremono_device_release method
+ Assign vdev.release to release method
+ Added gotos for better memory cleanup
- Removed incorrect kfrees in usb_release in v1
Changes in v1: 
+ Added k*allocs to raremono_device struct, and buffs
+ Added kfrees on error conditions in usb_probe
+ Added kfrees in usb_release
- Removed devm_k*allocs

 drivers/media/radio/radio-raremono.c | 31 +++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/media/radio/radio-raremono.c b/drivers/media/radio/radio-raremono.c
index 5e782b3c2fa9..a5b12372eccb 100644
--- a/drivers/media/radio/radio-raremono.c
+++ b/drivers/media/radio/radio-raremono.c
@@ -271,6 +271,15 @@ static int vidioc_g_frequency(struct file *file, void *priv,
 	return 0;
 }
 
+static void raremono_device_release(struct v4l2_device *v4l2_dev)
+{
+	struct raremono_device *radio = to_raremono_dev(v4l2_dev);
+
+	kfree(radio->buffer);
+	kfree(radio);
+}
+
+
 /* File system interface */
 static const struct v4l2_file_operations usb_raremono_fops = {
 	.owner		= THIS_MODULE,
@@ -295,12 +304,14 @@ static int usb_raremono_probe(struct usb_interface *intf,
 	struct raremono_device *radio;
 	int retval = 0;
 
-	radio = devm_kzalloc(&intf->dev, sizeof(struct raremono_device), GFP_KERNEL);
-	if (radio)
-		radio->buffer = devm_kmalloc(&intf->dev, BUFFER_LENGTH, GFP_KERNEL);
-
-	if (!radio || !radio->buffer)
+	radio = kzalloc(sizeof(struct raremono_device), GFP_KERNEL);
+	if (!radio)
+		return -ENOMEM;
+	radio->buffer = kmalloc(BUFFER_LENGTH, GFP_KERNEL);
+	if (!radio->buffer) {
+		kfree(radio);
 		return -ENOMEM;
+	}
 
 	radio->usbdev = interface_to_usbdev(intf);
 	radio->intf = intf;
@@ -324,7 +335,8 @@ static int usb_raremono_probe(struct usb_interface *intf,
 	if (retval != 3 ||
 	    (get_unaligned_be16(&radio->buffer[1]) & 0xfff) == 0x0242) {
 		dev_info(&intf->dev, "this is not Thanko's Raremono.\n");
-		return -ENODEV;
+		retval = -ENODEV;
+		goto free_mem;
 	}
 
 	dev_info(&intf->dev, "Thanko's Raremono connected: (%04X:%04X)\n",
@@ -333,7 +345,7 @@ static int usb_raremono_probe(struct usb_interface *intf,
 	retval = v4l2_device_register(&intf->dev, &radio->v4l2_dev);
 	if (retval < 0) {
 		dev_err(&intf->dev, "couldn't register v4l2_device\n");
-		return retval;
+		goto free_mem;
 	}
 
 	mutex_init(&radio->lock);
@@ -345,6 +357,7 @@ static int usb_raremono_probe(struct usb_interface *intf,
 	radio->vdev.ioctl_ops = &usb_raremono_ioctl_ops;
 	radio->vdev.lock = &radio->lock;
 	radio->vdev.release = video_device_release_empty;
+	radio->v4l2_dev.release = raremono_device_release;
 
 	usb_set_intfdata(intf, &radio->v4l2_dev);
 
@@ -360,6 +373,10 @@ static int usb_raremono_probe(struct usb_interface *intf,
 	}
 	dev_err(&intf->dev, "could not register video device\n");
 	v4l2_device_unregister(&radio->v4l2_dev);
+
+free_mem:
+	kfree(radio->buffer);
+	kfree(radio);
 	return retval;
 }
 
-- 
2.20.1