[PATCH] media: si470x: Fix use-after-free in si470x_int_in_callback()

[Shigeru Yoshida <syoshida@redhat.com>]

syzbot reported use-after-free in si470x_int_in_callback() [1].  This
indicates that urb->context, which contains struct si470x_device
object, is freed when si470x_int_in_callback() is called.

The cause of this issue is that si470x_int_in_callback() is called for
freed urb.

si470x_usb_driver_probe() calls si470x_start_usb(), which then calls
usb_submit_urb() and si470x_start().  If si470x_start_usb() fails,
si470x_usb_driver_probe() doesn't kill urb, but it just frees struct
si470x_device object, as depicted below:

si470x_usb_driver_probe()
  ...
  si470x_start_usb()
    ...
    usb_submit_urb()
    retval = si470x_start()
    return retval
  if (retval < 0)
    free struct si470x_device object, but don't kill urb

This patch fixes this issue by killing urb when si470x_start_usb()
fails and urb is submitted.  If si470x_start_usb() fails and urb is
not submitted, i.e. submitting usb fails, it just frees struct
si470x_device object.

Reported-by: syzbot+9ca7a12fd736d93e0232@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=94ed6dddd5a55e90fd4bab942aa4bb297741d977 [1]
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
 drivers/media/radio/si470x/radio-si470x-usb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/radio/si470x/radio-si470x-usb.c b/drivers/media/radio/si470x/radio-si470x-usb.c
index 6b2768623c88..aa7a580dbecc 100644
--- a/drivers/media/radio/si470x/radio-si470x-usb.c
+++ b/drivers/media/radio/si470x/radio-si470x-usb.c
@@ -727,8 +727,10 @@ static int si470x_usb_driver_probe(struct usb_interface *intf,
 
 	/* start radio */
 	retval = si470x_start_usb(radio);
-	if (retval < 0)
+	if (retval < 0 && !radio->int_in_running)
 		goto err_buf;
+	else if (retval < 0)	/* in case of radio->int_in_running == 1 */
+		goto err_all;
 
 	/* set initial frequency */
 	si470x_set_freq(radio, 87.5 * FREQ_MUL); /* available in all regions */
-- 
2.38.1