[PATCH 5.5 050/367] usb: gadget: f_ecm: Use atomic_t to track in-flight request

Greg Kroah-Hartman
2020-02-10T12:42:54Z

From: Bryan O'Donoghue <bryan.odonoghue@linaro.org>

commit d710562e01c48d59be3f60d58b7a85958b39aeda upstream.

Currently ecm->notify_req is used to flag when a request is in-flight.
ecm->notify_req is set to NULL and when a request completes it is
subsequently reset.

This is fundamentally buggy in that the unbind logic of the ECM driver will
unconditionally free ecm->notify_req leading to a NULL pointer dereference.

Fixes: da741b8c56d6 ("usb ethernet gadget: split CDC Ethernet function")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/gadget/function/f_ecm.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

--- a/drivers/usb/gadget/function/f_ecm.c
+++ b/drivers/usb/gadget/function/f_ecm.c
@@ -52,6 +52,7 @@ struct f_ecm {
struct usb_ep *notify;
struct usb_request *notify_req;
u8 notify_state;
+ atomic_t notify_count;
bool is_open;

/* FIXME is_open needs some irq-ish locking
@@ -380,7 +381,7 @@ static void ecm_do_notify(struct f_ecm *
int status;

/* notification already in flight? */
- if (!req)
+ if (atomic_read(&ecm->notify_count))
return;

event = req->buf;
@@ -420,10 +421,10 @@ static void ecm_do_notify(struct f_ecm *
event->bmRequestType = 0xA1;
event->wIndex = cpu_to_le16(ecm->ctrl_id);

- ecm->notify_req = NULL;
+ atomic_inc(&ecm->notify_count);
status = usb_ep_queue(ecm->notify, req, GFP_ATOMIC);
if (status < 0) {
- ecm->notify_req = req;
+ atomic_dec(&ecm->notify_count);
DBG(cdev, "notify --> %d\n", status);
}
}
@@ -448,17 +449,19 @@ static void ecm_notify_complete(struct u
switch (req->status) {
case 0:
/* no fault */
+ atomic_dec(&ecm->notify_count);
break;
case -ECONNRESET:
case -ESHUTDOWN:
+ atomic_set(&ecm->notify_count, 0);
ecm->notify_state = ECM_NOTIFY_NONE;
break;
default:
DBG(cdev, "event %02x --> %d\n",
event->bNotificationType, req->status);
+ atomic_dec(&ecm->notify_count);
break;
}
- ecm->notify_req = req;
ecm_do_notify(ecm);
}

@@ -907,6 +910,11 @@ static void ecm_unbind(struct usb_config

usb_free_all_descriptors(f);

+ if (atomic_read(&ecm->notify_count)) {
+ usb_ep_dequeue(ecm->notify, ecm->notify_req);
+ atomic_set(&ecm->notify_count, 0);
+ }
+
kfree(ecm->notify_req->buf);
usb_ep_free_request(ecm->notify, ecm->notify_req);
}