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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tuba Yavuz <tuba@ece.ufl.edu>,
        Felipe Balbi <felipe.balbi@linux.intel.com>
Subject: [PATCH 4.9 20/95] USB: gadget: f_midi: fixing a possible double-free in f_midi
Date:   Sun, 22 Apr 2018 15:52:49 +0200
Message-Id: <20180422135211.266586357@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yavuz, Tuba <tuba@ece.ufl.edu>

commit 7fafcfdf6377b18b2a726ea554d6e593ba44349f upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -389,7 +389,8 @@ static int f_midi_set_alt(struct usb_fun
 		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;
 		}
 	}
--- a/drivers/usb/gadget/u_f.h
+++ b/drivers/usb/gadget/u_f.h
@@ -64,7 +64,9 @@ struct usb_request *alloc_ep_req(struct
 /* 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);
 }