USB: core: only clean up what we allocated

[Andrey Konovalov <andreyknvl@google.com>]

On Tue, Dec 12, 2017 at 4:41 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> On Mon, 11 Dec 2017, Greg KH wrote:
>
>> From: Andrey Konovalov <andreyknvl@google.com>
>>
>> When cleaning up the configurations, make sure we only free the number
>> of configurations and interfaces that we could have allocated.
>>
>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> Cc: stable <stable@vger.kernel.org>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>
>> diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
>> index 55b198ba629b..93b38471754e 100644
>> --- a/drivers/usb/core/config.c
>> +++ b/drivers/usb/core/config.c
>> @@ -764,18 +764,21 @@ void usb_destroy_configuration(struct usb_device *dev)
>>               return;
>>
>>       if (dev->rawdescriptors) {
>> -             for (i = 0; i < dev->descriptor.bNumConfigurations; i++)
>> +             for (i = 0; i < dev->descriptor.bNumConfigurations &&
>> +                             i < USB_MAXCONFIG; i++)
>>                       kfree(dev->rawdescriptors[i]);
>>
>>               kfree(dev->rawdescriptors);
>>               dev->rawdescriptors = NULL;
>>       }
>>
>> -     for (c = 0; c < dev->descriptor.bNumConfigurations; c++) {
>> +     for (c = 0; c < dev->descriptor.bNumConfigurations &&
>> +                     c < USB_MAXCONFIG; c++) {
>>               struct usb_host_config *cf = &dev->config[c];
>>
>>               kfree(cf->string);
>> -             for (i = 0; i < cf->desc.bNumInterfaces; i++) {
>> +             for (i = 0; i < cf->desc.bNumInterfaces &&
>> +                             i < USB_MAXINTERFACES; i++) {
>>                       if (cf->intf_cache[i])
>>                               kref_put(&cf->intf_cache[i]->ref,
>>                                         usb_release_interface_cache);
>
> None of these changes are necessary.  The code is careful to reduce
> dev->descriptor.bNumConfigurations and config->desc.bNumInterfaces when
> necessary.
>
> In usb_get_configuration() (line 806 on my system):
>
>         if (ncfg > USB_MAXCONFIG) {
>                 dev_warn(ddev, "too many configurations: %d, "
>                     "using maximum allowed: %d\n", ncfg, USB_MAXCONFIG);
>                 dev->descriptor.bNumConfigurations = ncfg = USB_MAXCONFIG;
>         }
>
> In usb_parse_configuration() (line 676 on my system):
>
>         if (n != nintf)
>                 dev_warn(ddev, "config %d has %d interface%s, different from "
>                     "the descriptor's value: %d\n",
>                     cfgno, n, plural(n), nintf_orig);
>         else if (n == 0)
>                 dev_warn(ddev, "config %d has no interfaces?\n", cfgno);
>         config->desc.bNumInterfaces = nintf = n;

usb_parse_configuration() might return before reducing
config->desc.bNumInterfaces, and usb_destroy_configuration() is still
called in this case.

>
> Alan Stern
>
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