[PATCH v2] usb: gadget: f_midi: fix MIDI Streaming descriptor lengths

[PATCH v2] usb: gadget: f_midi: fix MIDI Streaming descriptor lengths

[John Keeping]

While the MIDI jacks are configured correctly, and the MIDIStreaming
endpoint descriptors are filled with the correct information,
bNumEmbMIDIJack and bLength are set incorrectly in these descriptors.

This does not matter when the numbers of in and out ports are equal, but
when they differ the host will receive broken descriptors with
uninitialized stack memory leaking into the descriptor for whichever
value is smaller.

The precise meaning of "in" and "out" in the port counts is not clearly
defined and can be confusing.  But elsewhere the driver consistently
uses this to match the USB meaning of IN and OUT viewed from the host,
so that "in" ports send data to the host and "out" ports receive data
from it.

Cc: stable@vger.kernel.org
Fixes: c8933c3f79568 ("USB: gadget: f_midi: allow a dynamic number of input and output ports")
Signed-off-by: John Keeping <jkeeping@inmusicbrands.com>
---
v2:
- Rewrite commit message to hopefully be clearer about what is going on
  with the meaning of in/out

 drivers/usb/gadget/function/f_midi.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 837fcdfa3840f..6cc3d86cb4774 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -1000,11 +1000,11 @@ static int f_midi_bind(struct usb_configuration *c, struct usb_function *f)
 	}
 
 	/* configure the endpoint descriptors ... */
-	ms_out_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->in_ports);
-	ms_out_desc.bNumEmbMIDIJack = midi->in_ports;
+	ms_out_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->out_ports);
+	ms_out_desc.bNumEmbMIDIJack = midi->out_ports;
 
-	ms_in_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->out_ports);
-	ms_in_desc.bNumEmbMIDIJack = midi->out_ports;
+	ms_in_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->in_ports);
+	ms_in_desc.bNumEmbMIDIJack = midi->in_ports;
 
 	/* ... and add them to the list */
 	endpoint_descriptor_index = i;
-- 
2.48.1

Re: [PATCH v2] usb: gadget: f_midi: fix MIDI Streaming descriptor lengths

[Takashi Iwai]

On Thu, 30 Jan 2025 20:50:34 +0100,
John Keeping wrote:
> 
> While the MIDI jacks are configured correctly, and the MIDIStreaming
> endpoint descriptors are filled with the correct information,
> bNumEmbMIDIJack and bLength are set incorrectly in these descriptors.
> 
> This does not matter when the numbers of in and out ports are equal, but
> when they differ the host will receive broken descriptors with
> uninitialized stack memory leaking into the descriptor for whichever
> value is smaller.
> 
> The precise meaning of "in" and "out" in the port counts is not clearly
> defined and can be confusing.  But elsewhere the driver consistently
> uses this to match the USB meaning of IN and OUT viewed from the host,
> so that "in" ports send data to the host and "out" ports receive data
> from it.
> 
> Cc: stable@vger.kernel.org
> Fixes: c8933c3f79568 ("USB: gadget: f_midi: allow a dynamic number of input and output ports")
> Signed-off-by: John Keeping <jkeeping@inmusicbrands.com>

Reviewed-by: Takashi Iwai <tiwai@suse.de>


Thanks!

Takashi