[PATCH v2] media: imon: fix use-after-free in display_close via dev_dbg

[Deepanshu Kartikey <kartikey406@gmail.com>]

ictx->dev is a raw pointer to the usb_interface's embedded device,
cached in imon_init_intf0() without taking a reference. On
disconnect, usb_disconnect() can drop the last reference on the
interface and free it while a userspace fd for /dev/lcd0 is still
open. When that fd is later closed, display_close() dereferences
the now-freed ictx->dev via dev_dbg(), causing a use-after-free.

Fix by pinning the device with get_device() when ictx->dev is
assigned, and releasing it with put_device() when ictx is freed.

Also drop the dev_dbg() in free_imon_context(), which only printed
a debug message and is no longer needed.

Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
Reported-by: syzbot+9bfac891bdd42eb708fc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9bfac891bdd42eb708fc
Link: http://lore.kernel.org/all/20260918054851.26083-1-kartikey406@gmail.com/T/ [v1]
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
v2:
- Remove the dev_dbg() in free_imon_context(), as suggested by
  Sean Young.
---
 drivers/media/rc/imon.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index 049a73b5f882..562a70186db4 100644
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -501,7 +501,7 @@ static void free_imon_context(struct imon_context *ictx)
 	usb_free_urb(ictx->rx_urb_intf1);
 	kfree_rcu(ictx, rcu);
 
-	dev_dbg(dev, "%s: iMON context freed\n", __func__);
+	put_device(dev);
 }
 
 /*
@@ -2253,7 +2253,7 @@ static struct imon_context *imon_init_intf0(struct usb_interface *intf,
 
 	mutex_lock(&ictx->lock);
 
-	ictx->dev = dev;
+	ictx->dev = get_device(dev);
 	ictx->usbdev_intf0 = interface_to_usbdev(intf);
 	ictx->rx_urb_intf0 = rx_urb;
 	ictx->tx_urb = tx_urb;
@@ -2314,6 +2314,7 @@ static struct imon_context *imon_init_intf0(struct usb_interface *intf,
 find_endpoint_failed:
 	mutex_unlock(&ictx->lock);
 	usb_free_urb(tx_urb);
+	put_device(ictx->dev);
 tx_urb_alloc_failed:
 	usb_free_urb(rx_urb);
 rx_urb_alloc_failed:
-- 
2.34.1