On Wed, 1 Sep 2010, Toby Gray wrote:
> Certain USB devices, such as the Nokia X6 mobile phone, don't expose any
> endpoint descriptors on some of their interfaces. If the ACM driver is forced
> to probe all interfaces on a device the a NULL pointer dereference will occur
> when the ACM driver attempts to use the endpoint of the alternative settings.
> One way to get the ACM driver to probe all the interfaces is by using the
> /sys/bus/usb/drivers/cdc_acm/new_id interface.
>
> This patch checks that the alternative settings and the associated endpoint
> pointer are non-NULL before using them.
The correct term is "alternate settings", not "alternative settings".
> Signed-off-by: Toby Gray <toby.gray@xxxxxxxxxxx>
> ---
> drivers/usb/class/cdc-acm.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 1833b3a..44bbeae 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -965,7 +965,9 @@ static int acm_probe(struct usb_interface *intf,
> }
>
> if (!buflen) {
> - if (intf->cur_altsetting->endpoint->extralen &&
> + if (intf->cur_altsetting &&
This test isn't needed. Interfaces always are in one altsetting or
another.
> + intf->cur_altsetting->endpoint &&
> + intf->cur_altsetting->endpoint->extralen &&
> intf->cur_altsetting->endpoint->extra) {
> dev_dbg(&intf->dev,
> "Seeking extra descriptors on endpoint\n");
Alan Stern
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