From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD750C43441 for ; Sun, 11 Nov 2018 20:33:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9686920818 for ; Sun, 11 Nov 2018 20:33:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9686920818 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731204AbeKLGXT (ORCPT ); Mon, 12 Nov 2018 01:23:19 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:50116 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730254AbeKLFsQ (ORCPT ); Mon, 12 Nov 2018 00:48:16 -0500 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1gLvsc-0000oN-1L; Sun, 11 Nov 2018 19:58:46 +0000 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gLvsZ-0001q5-In; Sun, 11 Nov 2018 19:58:43 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Sakari Ailus" , "Hans Verkuil" , "Mauro Carvalho Chehab" , "Laurent Pinchart" Date: Sun, 11 Nov 2018 19:49:05 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 323/366] media: v4l: event: Prevent freeing event subscriptions while accessed In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.61-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Sakari Ailus 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 Reviewed-by: Hans Verkuil Reviewed-by: Laurent Pinchart Fixes: c3b5b0241f62 ("V4L/DVB: V4L: Events: Add backend") Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Ben Hutchings --- 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(-) --- 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 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 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 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); + +out_unlock: + mutex_unlock(&fh->subscribe_lock); - return 0; + return ret; } EXPORT_SYMBOL_GPL(v4l2_event_subscribe); @@ -289,6 +287,8 @@ int v4l2_event_unsubscribe(struct v4l2_f 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_f if (sev && sev->ops && sev->ops->del) sev->ops->del(sev); + mutex_unlock(&fh->subscribe_lock); + kfree(sev); return 0; --- 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, st 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); --- 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;