From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mga05.intel.com ([192.55.52.43]:16073 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726599AbeKHVjj (ORCPT ); Thu, 8 Nov 2018 16:39:39 -0500 From: Sakari Ailus To: Ben Hutchings Cc: Dave Stevenson , Hans Verkuil , mchehab@kernel.org, linux-media@vger.kernel.org, stable@vger.kernel.org, #@punajuuri.localdomain, for@punajuuri.localdomain, 4.14@punajuuri.localdomain, and@punajuuri.localdomain, up@punajuuri.localdomain Subject: [PATCH v3.16 1/2] v4l: event: Prevent freeing event subscriptions while accessed Date: Thu, 8 Nov 2018 14:03:49 +0200 Message-Id: <20181108120350.17266-2-sakari.ailus@linux.intel.com> In-Reply-To: <20181108120350.17266-1-sakari.ailus@linux.intel.com> References: <20181108120350.17266-1-sakari.ailus@linux.intel.com> Sender: linux-media-owner@vger.kernel.org List-ID: [ upstream commit ad608fbcf166fec809e402d548761768f602702c ] 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 Reviewed-by: Hans Verkuil Reviewed-by: Laurent Pinchart Cc: stable@vger.kernel.org # for 4.14 and up Fixes: c3b5b0241f62 ("V4L/DVB: V4L: Events: Add backend") Signed-off-by: Mauro Carvalho Chehab --- drivers/media/v4l2-core/v4l2-event.c | 38 +++++++++++++++++++----------------- drivers/media/v4l2-core/v4l2-fh.c | 2 ++ include/media/v4l2-fh.h | 1 + 3 files changed, 23 insertions(+), 18 deletions(-) diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c index 8761aab99de95..fcf65f131a2ac 100644 --- a/drivers/media/v4l2-core/v4l2-event.c +++ b/drivers/media/v4l2-core/v4l2-event.c @@ -119,14 +119,6 @@ static void __v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *e if (sev == NULL) return; - /* - * If the event has been added to the fh->subscribed list, but its - * add op has not completed yet elems will be 0, treat this as - * not being subscribed. - */ - if (!sev->elems) - return; - /* Increase event sequence number on fh. */ fh->sequence++; @@ -209,6 +201,7 @@ int v4l2_event_subscribe(struct v4l2_fh *fh, struct v4l2_subscribed_event *sev, *found_ev; unsigned long flags; unsigned i; + int ret = 0; if (sub->type == V4L2_EVENT_ALL) return -EINVAL; @@ -226,31 +219,36 @@ int v4l2_event_subscribe(struct v4l2_fh *fh, sev->flags = sub->flags; sev->fh = fh; sev->ops = ops; + sev->elems = elems; + + mutex_lock(&fh->subscribe_lock); spin_lock_irqsave(&fh->vdev->fh_lock, flags); found_ev = v4l2_event_subscribed(fh, sub->type, sub->id); - if (!found_ev) - list_add(&sev->list, &fh->subscribed); spin_unlock_irqrestore(&fh->vdev->fh_lock, flags); if (found_ev) { + /* Already listening */ kfree(sev); - return 0; /* Already listening */ + goto out_unlock; } if (sev->ops && sev->ops->add) { - int ret = sev->ops->add(sev, elems); + ret = sev->ops->add(sev, elems); if (ret) { - sev->ops = NULL; - v4l2_event_unsubscribe(fh, sub); - return ret; + kfree(sev); + goto out_unlock; } } - /* Mark as ready for use */ - sev->elems = elems; + spin_lock_irqsave(&fh->vdev->fh_lock, flags); + list_add(&sev->list, &fh->subscribed); + spin_unlock_irqrestore(&fh->vdev->fh_lock, flags); - return 0; +out_unlock: + mutex_unlock(&fh->subscribe_lock); + + return ret; } EXPORT_SYMBOL_GPL(v4l2_event_subscribe); @@ -289,6 +287,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh, return 0; } + mutex_lock(&fh->subscribe_lock); + spin_lock_irqsave(&fh->vdev->fh_lock, flags); sev = v4l2_event_subscribed(fh, sub->type, sub->id); @@ -306,6 +306,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh, if (sev && sev->ops && sev->ops->del) sev->ops->del(sev); + mutex_unlock(&fh->subscribe_lock); + kfree(sev); return 0; diff --git a/drivers/media/v4l2-core/v4l2-fh.c b/drivers/media/v4l2-core/v4l2-fh.c index e57c002b41506..573ec2f192d44 100644 --- a/drivers/media/v4l2-core/v4l2-fh.c +++ b/drivers/media/v4l2-core/v4l2-fh.c @@ -42,6 +42,7 @@ void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev) INIT_LIST_HEAD(&fh->available); INIT_LIST_HEAD(&fh->subscribed); fh->sequence = -1; + mutex_init(&fh->subscribe_lock); } EXPORT_SYMBOL_GPL(v4l2_fh_init); @@ -88,6 +89,7 @@ void v4l2_fh_exit(struct v4l2_fh *fh) if (fh->vdev == NULL) return; v4l2_event_unsubscribe_all(fh); + mutex_destroy(&fh->subscribe_lock); fh->vdev = NULL; } EXPORT_SYMBOL_GPL(v4l2_fh_exit); diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h index 803516775162d..a2777a324e083 100644 --- a/include/media/v4l2-fh.h +++ b/include/media/v4l2-fh.h @@ -41,6 +41,7 @@ struct v4l2_fh { /* Events */ wait_queue_head_t wait; + struct mutex subscribe_lock; struct list_head subscribed; /* Subscribed events */ struct list_head available; /* Dequeueable event */ unsigned int navailable; -- 2.11.0