Re: USB: gadget: f_midi: fixing a possible double-free in f_midi

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Aug 20, 2019 at 10:45:13AM -0700, Mark Salyzyn wrote:
> From: "Yavuz, Tuba" <tuba@ece.ufl.edu>
> 
> cherry pick from commit 7fafcfdf6377b18b2a726ea554d6e593ba44349f
> ("USB: gadget: f_midi: fixing a possible double-free in f_midi")
> Removing 'return err;' from conflict.
> 
> It looks like there is a possibility of a double-free vulnerability on an
> error path of the f_midi_set_alt function in the f_midi driver. If the
> path is feasible then free_ep_req gets called twice:
> 
>          req->complete = f_midi_complete;
>          err = usb_ep_queue(midi->out_ep, req, GFP_ATOMIC);
>             => ...
>              usb_gadget_giveback_request
>                =>
>                  f_midi_complete (CALLBACK)
>                    (inside f_midi_complete, for various cases of status)
>                    free_ep_req(ep, req); // first kfree
>          if (err) {
>                  ERROR(midi, "%s: couldn't enqueue request: %d\n",
>                              midi->out_ep->name, err);
>                  free_ep_req(midi->out_ep, req); // second kfree
>                  return err;
>          }
> 
> The double-free possibility was introduced with commit ad0d1a058eac
> ("usb: gadget: f_midi: fix leak on failed to enqueue out requests").
> 
> Found by MOXCAFE tool.
> 
> Signed-off-by: Tuba Yavuz <tuba@ece.ufl.edu>
> Fixes: ad0d1a058eac ("usb: gadget: f_midi: fix leak on failed to enqueue out requests")
> Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
> Cc: stable <stable@vger.kernel.org> # 4.4.y

No signed-off-by from you?

Anyway, this is already in the 4.4.y queue and will be in the next
release.

thanks,

greg k-h