[alsa-devel] [PATCH] USB: fix gathering of interface associations

[Daniel Mack]

On 12.06.2012 20:23, Daniel Mack wrote:
> TEAC's UD-H01 (and probably other devices) have a gap in the interface
> number allocation of their descriptors:

I now got a report from Sergio Tabanelli who tried this patch on real
hardware, and he confirmed the fix. I added some more people to the
patch description and copied stable@ as well.

Greg, can can this go through your tree?


Daniel


> 
>   Configuration Descriptor:
>     bLength                 9
>     bDescriptorType         2
>     wTotalLength          220
>     bNumInterfaces          3
>     [...]
>     Interface Descriptor:
>       bLength                 9
>       bDescriptorType         4
>       bInterfaceNumber        0
>       bAlternateSetting       0
>       [...]
>     Interface Association:
>       bLength                 8
>       bDescriptorType        11
>       bFirstInterface         2
>       bInterfaceCount         2
>       bFunctionClass          1 Audio
>       bFunctionSubClass       0
>       bFunctionProtocol      32
>       iFunction               4
>     Interface Descriptor:
>       bLength                 9
>       bDescriptorType         4
>       bInterfaceNumber        2
>       bAlternateSetting       0
>       [...]
> 
> Once a configuration is selected, usb_set_configuration() walks the
> known interfaces of a given configuration and calls find_iad() on
> each of them to set the interface association pointer the interface
> is included in.
> 
> The problem here is that the loop variable is taken for the interface
> number in the comparison logic that gathers the association. Which is
> fine as long as the descriptors are sane.
> 
> In the case above, however, the logic gets out of sync and the
> interface association fields of all interfaces beyond the interface
> number gap are wrong.
> 
> Fix this by passing the interface's bInterfaceNumber to find_iad()
> instead.
> 
> Signed-off-by: Daniel Mack <zonque at gmail.com>
> Reported-by: bEN <ml_all at circa.be>
> Reported-by: Ivan Perrone <ivanperrone at hotmail.com>
> ---
> 
> This patch has been tested on a virtual USB device emulated in QEMU.
> I'm still waiting for test results based on real hardware, but the bug
> is rather obvious is and the fix really simple.
> 
> Daniel
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