[PATCH] media: em28xx: reject audio endpoint with zero packet size

[Xiang Mei]

em28xx_audio_urb_init() divides by the audio endpoint's wMaxPacketSize
without checking it, so a USB device that declares a zero-sized audio
endpoint divides by zero at probe time.

Reject a zero-sized audio endpoint like a missing one; the caller already
unwinds on a negative return.

  Oops: divide error: 0000 [#1] SMP NOPTI
  Workqueue: usb_hub_wq hub_event
  RIP: 0010:em28xx_audio_init (drivers/media/usb/em28xx/em28xx-audio.c:718)
  Call Trace:
   em28xx_init_extension (drivers/media/usb/em28xx/em28xx-core.c:1248)
   em28xx_init_dev.isra.0 (drivers/media/usb/em28xx/em28xx-cards.c:3887)
   em28xx_usb_probe (drivers/media/usb/em28xx/em28xx-cards.c:4258)
   usb_probe_interface (drivers/usb/core/driver.c:396)
   ...
   usb_set_configuration (drivers/usb/core/message.c:2268)
   usb_generic_driver_probe (drivers/usb/core/generic.c:250)
   usb_probe_device (drivers/usb/core/driver.c:291)
   ...
   usb_new_device (drivers/usb/core/hub.c:2703)
   hub_event (drivers/usb/core/hub.c:5961)
   process_one_work (kernel/workqueue.c:3322)
   worker_thread (kernel/workqueue.c:3486)
   kthread (kernel/kthread.c:436)
   ret_from_fork (arch/x86/kernel/process.c:158)
   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
  Kernel panic - not syncing: Fatal exception

Fixes: 1b3fd2d34266 ("[media] em28xx-audio: don't hardcode audio URB calculus")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: co+9782320f78c23f40@xxxxxxx
Closes: https://lore.kernel.org/all/51lCz4R7QyTUKbh4mhXNaNzX0evpk0siOzbh%40bugs.sh/
Assisted-by: Claude:claude-opus-5
Signed-off-by: Xiang Mei <xmei5@xxxxxxx>
---
 drivers/media/usb/em28xx/em28xx-audio.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/media/usb/em28xx/em28xx-audio.c b/drivers/media/usb/em28xx/em28xx-audio.c
index ccff6be5599e..7f0c5826ce5e 100644
--- a/drivers/media/usb/em28xx/em28xx-audio.c
+++ b/drivers/media/usb/em28xx/em28xx-audio.c
@@ -693,6 +693,13 @@ static int em28xx_audio_urb_init(struct em28xx *dev)
 	}
 
 	ep_size = em28xx_audio_ep_packet_size(udev, ep);
+	if (ep_size == 0) {
+		dev_err(&dev->intf->dev,
+			"Audio endpoint 0x%02x has a zero packet size\n",
+			EM28XX_EP_AUDIO);
+		return -ENODEV;
+	}
+
 	interval = 1 << (ep->bInterval - 1);
 
 	dev_info(&dev->intf->dev,
-- 
2.43.0