patch "USB: gadget: f_midi: fixing a possible double-free in f_midi" added to usb-testing

This is a note to let you know that I've just added the patch titled

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

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the usb-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

From: "Yavuz, Tuba" <[email protected]>
Date: Fri, 23 Mar 2018 17:00:38 +0000
Subject: USB: gadget: f_midi: fixing a possible double-free in f_midi

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.

---
 drivers/usb/gadget/function/f_midi.c | 3 ++-
 drivers/usb/gadget/u_f.h             | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

index 4eb96b91cc40..e8f35db42394 100644
@@ -404,7 +404,8 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 		if (err) {
 			ERROR(midi, "%s: couldn't enqueue request: %d\n",
 				    midi->out_ep->name, err);
-			free_ep_req(midi->out_ep, req);
+			if (req->buf != NULL)
+				free_ep_req(midi->out_ep, req);
 			return err;
 		}
 	}

index c3fbef2bb5db..09f90447fed5 100644
@@ -61,7 +61,9 @@ struct usb_request *alloc_ep_req(struct usb_ep *ep, size_t len);
 /* Frees a usb_request previously allocated by alloc_ep_req() */
 static inline void free_ep_req(struct usb_ep *ep, struct usb_request *req)
 {
+	WARN_ON(req->buf == NULL);
 	kfree(req->buf);
+	req->buf = NULL;
 	usb_ep_free_request(ep, req);
 }
 

2.16.2