[PATCH 4.4 35/78] USB: gadget: f_midi: fixing a possible double-free in f_midi

Greg Kroah-Hartman
2019-08-22T17:45:59Z

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>
Cc: Guenter Roeck <linux@roeck-us.net>
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
@@ -366,7 +366,8 @@ 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
@@ -65,7 +65,9 @@ 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);
}