From nobody Fri Apr 10 20:21:50 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 B3E3CC25B0E for ; Fri, 19 Aug 2022 07:12:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345983AbiHSHMj (ORCPT ); Fri, 19 Aug 2022 03:12:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346491AbiHSHMg (ORCPT ); Fri, 19 Aug 2022 03:12:36 -0400 Received: from mail.ispras.ru (mail.ispras.ru [83.149.199.84]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41D74E2C4D; Fri, 19 Aug 2022 00:12:34 -0700 (PDT) Received: from localhost.localdomain (unknown [46.242.14.200]) by mail.ispras.ru (Postfix) with ESMTPSA id 6AACD40737D3; Fri, 19 Aug 2022 07:12:32 +0000 (UTC) From: Fedor Pchelkin To: stable@vger.kernel.org, Greg Kroah-Hartman Cc: Fedor Pchelkin , Tadeusz Struk , Peter Zijlstra , Dietmar Eggemann , linux-kernel@vger.kernel.org, Alexey Khoroshilov , ldv-project@linuxtesting.org, syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Subject: [PATCH 5.10 1/1] sched/fair: Fix fault in reweight_entity Date: Fri, 19 Aug 2022 10:11:40 +0300 Message-Id: <20220819071140.35728-2-pchelkin@ispras.ru> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220819071140.35728-1-pchelkin@ispras.ru> References: <20220819071140.35728-1-pchelkin@ispras.ru> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tadeusz Struk commit 13765de8148f71fa795e0a6607de37c49ea5915a upstream. Syzbot found a GPF in reweight_entity. This has been bisected to commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group") There=C2=A0is a race between sched_post_fork() and setpriority(PRIO_PGRP) within a thread group that causes a null-ptr-deref=C2=A0in reweight_entity() in CFS. The scenario is that the main process spawns number of new threads, which then call setpriority(PRIO_PGRP, 0, -20), wait, and exit. For each of the new threads the copy_process() gets invoked, which adds the new task_struct and calls sched_post_fork() for it. In the above scenario there is a possibility that setpriority(PRIO_PGRP) and set_one_prio() will be called for a thread in the group that is just being created by copy_process(), and for which the sched_post_fork() has not been executed yet. This will trigger a null pointer dereference in reweight_entity(),=C2=A0as it will try to access the run queue pointer, which hasn't been set. Before the mentioned change the cfs_rq pointer for the task has been set in sched_fork(), which is called much earlier in copy_process(), before the new task is added to the thread_group. Now it is done in the sched_post_fork(), which is called after that. To fix the issue the remove the update_load param from the update_load param() function and call reweight_task() only if the task flag doesn't have the TASK_NEW flag set. Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sche= d_task_group") Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dietmar Eggemann Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20220203161846.1160750-1-tadeusz.struk@lina= ro.org Signed-off-by: Fedor Pchelkin --- 5.10 adaptation: Replaced a task_struct field '__state' with 'state'=20 kernel/sched/core.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e437d946b27b..86c5e08b393b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -844,8 +844,9 @@ int tg_nop(struct task_group *tg, void *data) } #endif =20 -static void set_load_weight(struct task_struct *p, bool update_load) +static void set_load_weight(struct task_struct *p) { + bool update_load =3D !(READ_ONCE(p->state) & TASK_NEW); int prio =3D p->static_prio - MAX_RT_PRIO; struct load_weight *load =3D &p->se.load; =20 @@ -3262,7 +3263,7 @@ int sched_fork(unsigned long clone_flags, struct task= _struct *p) p->static_prio =3D NICE_TO_PRIO(0); =20 p->prio =3D p->normal_prio =3D p->static_prio; - set_load_weight(p, false); + set_load_weight(p); =20 /* * We don't need the reset flag anymore after the fork. It has @@ -5011,7 +5012,7 @@ void set_user_nice(struct task_struct *p, long nice) put_prev_task(rq, p); =20 p->static_prio =3D NICE_TO_PRIO(nice); - set_load_weight(p, true); + set_load_weight(p); old_prio =3D p->prio; p->prio =3D effective_prio(p); =20 @@ -5184,7 +5185,7 @@ static void __setscheduler_params(struct task_struct = *p, */ p->rt_priority =3D attr->sched_priority; p->normal_prio =3D normal_prio(p); - set_load_weight(p, true); + set_load_weight(p); } =20 /* @@ -7189,7 +7190,7 @@ void __init sched_init(void) atomic_set(&rq->nr_iowait, 0); } =20 - set_load_weight(&init_task, false); + set_load_weight(&init_task); =20 /* * The boot idle thread does lazy MMU switching as well: --=20 2.25.1