From nobody Sun Feb 8 07:59:03 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10723EB64DA for ; Mon, 10 Jul 2023 08:14:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232798AbjGJIOX (ORCPT ); Mon, 10 Jul 2023 04:14:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232938AbjGJINq (ORCPT ); Mon, 10 Jul 2023 04:13:46 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0EE0DDF; Mon, 10 Jul 2023 01:13:45 -0700 (PDT) Date: Mon, 10 Jul 2023 08:13:42 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1688976823; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=w4fjr/kcovinH/IMzg7clUPUhwYxaQ0rX1o/NlWtv2I=; b=xAN99qqX1BoJZrohuoYPYVGDpIonWaj3jeSHfvJ5vNAmnSxS6j0J5KsqyxPKnNI7LDmleh EFxwb52UJFdypLKmxfFvfgAEGDWUdPTyN1q3fZ1uKpYnif9jrmAlvAinEVlAgMiMFRl4gC IXybSgv8xWGhPuSOJhjQ8JGG91ncvQSe5bLlpI5EJOwrlIUFTskEs3cnal7mNOBAPuHPRM HPP6XMng18ED7u/URCQy/4SQSOuRMdB5KSNzEURZ0mK+0uTKRZPBU+Ny0BFNw04HeeGtTC xPa3F6sD91k5X/2ZS3/7uQGRO9yffeO9efzyMwQc23Fb/RmolHl0fDQdz0HP1g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1688976823; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=w4fjr/kcovinH/IMzg7clUPUhwYxaQ0rX1o/NlWtv2I=; b=i/kcXMv03TSszfKwbfAVVZToqqurdKWvhTaaZxgWSM1rD2kunXWP/+8PUjfeD1Ck0wW6ke 07F0hDI34E4CSjAQ== From: "tip-bot2 for Suren Baghdasaryan" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/urgent] sched/psi: use kernfs polling functions for PSI trigger polling Cc: Lu Jialin , Suren Baghdasaryan , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230630005612.1014540-1-surenb@google.com> References: <20230630005612.1014540-1-surenb@google.com> MIME-Version: 1.0 Message-ID: <168897682262.404.10162402491972251982.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/urgent branch of tip: Commit-ID: aff037078ecaecf34a7c2afab1341815f90fba5e Gitweb: https://git.kernel.org/tip/aff037078ecaecf34a7c2afab1341815f= 90fba5e Author: Suren Baghdasaryan AuthorDate: Thu, 29 Jun 2023 17:56:12 -07:00 Committer: Peter Zijlstra CommitterDate: Mon, 10 Jul 2023 09:52:30 +02:00 sched/psi: use kernfs polling functions for PSI trigger polling Destroying psi trigger in cgroup_file_release causes UAF issues when a cgroup is removed from under a polling process. This is happening because cgroup removal causes a call to cgroup_file_release while the actual file is still alive. Destroying the trigger at this point would also destroy its waitqueue head and if there is still a polling process on that file accessing the waitqueue, it will step on the freed pointer: do_select vfs_poll do_rmdir cgroup_rmdir kernfs_drain_open_files cgroup_file_release cgroup_pressure_release psi_trigger_destroy wake_up_pollfree(&t->event_wait) // vfs_poll is unblocked synchronize_rcu kfree(t) poll_freewait -> UAF access to the trigger's waitqueue head Patch [1] fixed this issue for epoll() case using wake_up_pollfree(), however the same issue exists for synchronous poll() case. The root cause of this issue is that the lifecycles of the psi trigger's waitqueue and of the file associated with the trigger are different. Fix this by using kernfs_generic_poll function when polling on cgroup-specific psi triggers. It internally uses kernfs_open_node->poll waitqueue head with its lifecycle tied to the file's lifecycle. This also renders the fix in [1] obsolete, so revert it. [1] commit c2dbe32d5db5 ("sched/psi: Fix use-after-free in ep_remove_wait_q= ueue()") Fixes: 0e94682b73bf ("psi: introduce psi monitor") Closes: https://lore.kernel.org/all/20230613062306.101831-1-lujialin4@huawe= i.com/ Reported-by: Lu Jialin Signed-off-by: Suren Baghdasaryan Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230630005612.1014540-1-surenb@google.com --- include/linux/psi.h | 5 +++-- include/linux/psi_types.h | 3 +++ kernel/cgroup/cgroup.c | 2 +- kernel/sched/psi.c | 29 +++++++++++++++++++++-------- 4 files changed, 28 insertions(+), 11 deletions(-) diff --git a/include/linux/psi.h b/include/linux/psi.h index ab26200..e074587 100644 --- a/include/linux/psi.h +++ b/include/linux/psi.h @@ -23,8 +23,9 @@ void psi_memstall_enter(unsigned long *flags); void psi_memstall_leave(unsigned long *flags); =20 int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res= ); -struct psi_trigger *psi_trigger_create(struct psi_group *group, - char *buf, enum psi_res res, struct file *file); +struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, + enum psi_res res, struct file *file, + struct kernfs_open_file *of); void psi_trigger_destroy(struct psi_trigger *t); =20 __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file, diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h index 040c089..f1fd3a8 100644 --- a/include/linux/psi_types.h +++ b/include/linux/psi_types.h @@ -137,6 +137,9 @@ struct psi_trigger { /* Wait queue for polling */ wait_queue_head_t event_wait; =20 + /* Kernfs file for cgroup triggers */ + struct kernfs_open_file *of; + /* Pending event flag */ int event; =20 diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index bfe3cd8..f55a40d 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3730,7 +3730,7 @@ static ssize_t pressure_write(struct kernfs_open_file= *of, char *buf, } =20 psi =3D cgroup_psi(cgrp); - new =3D psi_trigger_create(psi, buf, res, of->file); + new =3D psi_trigger_create(psi, buf, res, of->file, of); if (IS_ERR(new)) { cgroup_put(cgrp); return PTR_ERR(new); diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 81fca77..9bb3f2b 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -493,8 +493,12 @@ static u64 update_triggers(struct psi_group *group, u6= 4 now, bool *update_total, continue; =20 /* Generate an event */ - if (cmpxchg(&t->event, 0, 1) =3D=3D 0) - wake_up_interruptible(&t->event_wait); + if (cmpxchg(&t->event, 0, 1) =3D=3D 0) { + if (t->of) + kernfs_notify(t->of->kn); + else + wake_up_interruptible(&t->event_wait); + } t->last_event_time =3D now; /* Reset threshold breach flag once event got generated */ t->pending_event =3D false; @@ -1271,8 +1275,9 @@ int psi_show(struct seq_file *m, struct psi_group *gr= oup, enum psi_res res) return 0; } =20 -struct psi_trigger *psi_trigger_create(struct psi_group *group, - char *buf, enum psi_res res, struct file *file) +struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, + enum psi_res res, struct file *file, + struct kernfs_open_file *of) { struct psi_trigger *t; enum psi_states state; @@ -1331,7 +1336,9 @@ struct psi_trigger *psi_trigger_create(struct psi_gro= up *group, =20 t->event =3D 0; t->last_event_time =3D 0; - init_waitqueue_head(&t->event_wait); + t->of =3D of; + if (!of) + init_waitqueue_head(&t->event_wait); t->pending_event =3D false; t->aggregator =3D privileged ? PSI_POLL : PSI_AVGS; =20 @@ -1388,7 +1395,10 @@ void psi_trigger_destroy(struct psi_trigger *t) * being accessed later. Can happen if cgroup is deleted from under a * polling process. */ - wake_up_pollfree(&t->event_wait); + if (t->of) + kernfs_notify(t->of->kn); + else + wake_up_interruptible(&t->event_wait); =20 if (t->aggregator =3D=3D PSI_AVGS) { mutex_lock(&group->avgs_lock); @@ -1465,7 +1475,10 @@ __poll_t psi_trigger_poll(void **trigger_ptr, if (!t) return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; =20 - poll_wait(file, &t->event_wait, wait); + if (t->of) + kernfs_generic_poll(t->of, wait); + else + poll_wait(file, &t->event_wait, wait); =20 if (cmpxchg(&t->event, 1, 0) =3D=3D 1) ret |=3D EPOLLPRI; @@ -1535,7 +1548,7 @@ static ssize_t psi_write(struct file *file, const cha= r __user *user_buf, return -EBUSY; } =20 - new =3D psi_trigger_create(&psi_system, buf, res, file); + new =3D psi_trigger_create(&psi_system, buf, res, file, NULL); if (IS_ERR(new)) { mutex_unlock(&seq->lock); return PTR_ERR(new);