media: v4l: event: Prevent freeing event subscriptions while accessed
commit ad608fbcf166fec809e402d548761768f602702c upstream.
The event subscriptions are added to the subscribed event list while
holding a spinlock, but that lock is subsequently released while still
accessing the subscription object. This makes it possible to unsubscribe
the event --- and freeing the subscription object's memory --- while
the subscription object is simultaneously accessed.
Prevent this by adding a mutex to serialise the event subscription and
unsubscription. This also gives a guarantee to the callback ops that the
add op has returned before the del op is called.
This change also results in making the elems field less special:
subscriptions are only added to the event list once they are fully
initialised.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: stable@vger.kernel.org # for 4.14 and up
Fixes: c3b5b0241f
("V4L/DVB: V4L: Events: Add backend")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
a488247ff6
commit
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@ -119,14 +119,6 @@ static void __v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *e
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if (sev == NULL)
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return;
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/*
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* If the event has been added to the fh->subscribed list, but its
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* add op has not completed yet elems will be 0, treat this as
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* not being subscribed.
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*/
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if (!sev->elems)
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return;
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/* Increase event sequence number on fh. */
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fh->sequence++;
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@ -209,6 +201,7 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
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struct v4l2_subscribed_event *sev, *found_ev;
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unsigned long flags;
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unsigned i;
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int ret = 0;
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if (sub->type == V4L2_EVENT_ALL)
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return -EINVAL;
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@ -226,31 +219,36 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
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sev->flags = sub->flags;
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sev->fh = fh;
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sev->ops = ops;
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sev->elems = elems;
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mutex_lock(&fh->subscribe_lock);
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spin_lock_irqsave(&fh->vdev->fh_lock, flags);
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found_ev = v4l2_event_subscribed(fh, sub->type, sub->id);
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if (!found_ev)
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list_add(&sev->list, &fh->subscribed);
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spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
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if (found_ev) {
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/* Already listening */
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kfree(sev);
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return 0; /* Already listening */
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goto out_unlock;
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}
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if (sev->ops && sev->ops->add) {
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int ret = sev->ops->add(sev, elems);
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ret = sev->ops->add(sev, elems);
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if (ret) {
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sev->ops = NULL;
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v4l2_event_unsubscribe(fh, sub);
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return ret;
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kfree(sev);
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goto out_unlock;
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}
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}
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/* Mark as ready for use */
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sev->elems = elems;
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spin_lock_irqsave(&fh->vdev->fh_lock, flags);
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list_add(&sev->list, &fh->subscribed);
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spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
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return 0;
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out_unlock:
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mutex_unlock(&fh->subscribe_lock);
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return ret;
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}
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EXPORT_SYMBOL_GPL(v4l2_event_subscribe);
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@ -289,6 +287,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
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return 0;
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}
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mutex_lock(&fh->subscribe_lock);
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spin_lock_irqsave(&fh->vdev->fh_lock, flags);
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sev = v4l2_event_subscribed(fh, sub->type, sub->id);
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@ -307,6 +307,7 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
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sev->ops->del(sev);
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kfree(sev);
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mutex_unlock(&fh->subscribe_lock);
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return 0;
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}
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@ -42,6 +42,7 @@ void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev)
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INIT_LIST_HEAD(&fh->available);
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INIT_LIST_HEAD(&fh->subscribed);
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fh->sequence = -1;
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mutex_init(&fh->subscribe_lock);
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}
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EXPORT_SYMBOL_GPL(v4l2_fh_init);
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@ -88,6 +89,7 @@ void v4l2_fh_exit(struct v4l2_fh *fh)
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if (fh->vdev == NULL)
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return;
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v4l2_event_unsubscribe_all(fh);
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mutex_destroy(&fh->subscribe_lock);
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fh->vdev = NULL;
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}
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EXPORT_SYMBOL_GPL(v4l2_fh_exit);
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@ -41,6 +41,7 @@ struct v4l2_fh {
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wait_queue_head_t wait;
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struct list_head subscribed; /* Subscribed events */
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struct list_head available; /* Dequeueable event */
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struct mutex subscribe_lock;
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unsigned int navailable;
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u32 sequence;
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};
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