From nobody Tue Jun 30 04:38:01 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 6E7CDC433EF for ; Tue, 25 Jan 2022 19:35:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230303AbiAYTfg (ORCPT ); Tue, 25 Jan 2022 14:35:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230205AbiAYTe1 (ORCPT ); Tue, 25 Jan 2022 14:34:27 -0500 Received: from mail-pf1-x429.google.com (mail-pf1-x429.google.com [IPv6:2607:f8b0:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A69D3C061747 for ; Tue, 25 Jan 2022 11:34:25 -0800 (PST) Received: by mail-pf1-x429.google.com with SMTP id u130so16440537pfc.2 for ; Tue, 25 Jan 2022 11:34:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=wqkKZwea4Ntd1UMLoEnxDe91teRkaMMO7ADnYpsEdMY=; b=Xax9igYolzgTI16rjcvA8qDy9hafAlD+40MG99uerzRhh0xcnwKx0vFFRpRLKXYeH8 tXPv3lZv2wlrAdPIBPf33UKrEC6hN3ZTkTy65/mll1hln7phNHyMfgImIu018DPHuTHC lMkw2UyJ6vdDWTzyFzUHtVqaKKSjOFKPDm+o57lPjotAHyTHwxSAa3fQooLvtqb4LXb0 5s+Dym2nVR1PFfXPpg/9jAMYwRTxQfmTaMz7PQuafw4Le9KX3N8RI3n0SGZtqocxO4qX p6d6ohiKn3Z8GugQHJq2QwVTs442Q97jxAXKnld2tZVN1zn4e0zZ8FmRxhTM7HwuTF7U F4TQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=wqkKZwea4Ntd1UMLoEnxDe91teRkaMMO7ADnYpsEdMY=; b=qkPcV7bfukEKm1wZZ8R8EonqaExH9MKn1i3IoaWY2kG+mTJrZUpJzhDWdw1R5l0JTE 6TR1uwWiCtPHZnlzAqSC2zFUmSrL4W+yYA4bs29pJMrp10U2vWyZ/f2K4Ybf3Sak7lG2 Hxzur17dljCdWdfGbkoJ8Ic9owMEfq2upuEF1uYzPLz1xibHWS4+Jl59+acrOCsucMRR qWRTKIH1qZY3t0fGn93g2xOASIKkefJW2a0fMTv9BKs12zHRW0VjNw6DPoZN6ix2Oz1s Bpo9wxlNcyBxVXYXUUmjKd9l3N/9XyLiFVLC3lfOCk+kHTaoSzSw/37A/9BVbgp4FqNF NqQg== X-Gm-Message-State: AOAM530X/NDs9wpESpvTaQLCEMNsU/wwXb63PYsrlO02Q+1vMDUufxZ+ tYuHNBLYsWtj2JMlwils1eobVA== X-Google-Smtp-Source: ABdhPJwKn4xsubm3B306tmrdkEHk+6IyVkLSe3+CfFCGvzbf6On+fSFVFQ3hGvWDObdK1oO/yyE/RQ== X-Received: by 2002:a05:6a00:1312:b0:4c4:cffa:a4c0 with SMTP id j18-20020a056a00131200b004c4cffaa4c0mr19606314pfu.79.1643139265175; Tue, 25 Jan 2022 11:34:25 -0800 (PST) Received: from localhost.localdomain ([50.39.160.154]) by smtp.gmail.com with ESMTPSA id q7sm19499854pfs.32.2022.01.25.11.34.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jan 2022 11:34:24 -0800 (PST) From: Tadeusz Struk To: peterz@infradead.org Cc: Tadeusz Struk , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Zhang Qiao , Daniel Jordan , stable@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Subject: [PATCH v3] sched/fair: Fix fault in reweight_entity Date: Tue, 25 Jan 2022 11:34:03 -0800 Message-Id: <20220125193403.778497-1-tadeusz.struk@linaro.org> X-Mailer: git-send-email 2.34.1 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 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, whi= ch hasn't been set. This results it a crash as shown below: KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7] CPU: 0 PID: 2392 Comm: reduced_repro Not tainted 5.16.0-11201-gb42c5a161ea3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35 0= 4/01/2014 RIP: 0010:reweight_entity+0x15d/0x440 RSP: 0018:ffffc900035dfcf8 EFLAGS: 00010006 Call Trace: reweight_task+0xde/0x1c0 set_load_weight+0x21c/0x2b0 set_user_nice.part.0+0x2d1/0x519 set_user_nice.cold+0x8/0xd set_one_prio+0x24f/0x263 __do_sys_setpriority+0x2d3/0x640 __x64_sys_setpriority+0x84/0x8b do_syscall_64+0x35/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com ---[ end trace 9dc80a9d378ed00a ]--- 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 update_load condition passed to set_load_weight() in set_user_nice() and __sched_setscheduler() has been changed from always true to true if the task->state !=3D TASK_NEW. Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: Zhang Qiao Cc: Daniel Jordan Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org Link: https://syzkaller.appspot.com/bug?id=3D9d9c27adc674e3a7932b22b61c79a0= 2da82cbdc1 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 --- Changes in v3: - Removed the new check and changed the update_load condition from always true to true if p->state !=3D TASK_NEW Changes in v2: - Added a check in=C2=A0set_user_nice(), and return from there if the task is not fully setup instead of returning from reweight_entity() --- --- kernel/sched/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 848eaa0efe0e..3d7ede06b971 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6921,7 +6921,7 @@ 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, !(READ_ONCE(p->__state) & TASK_NEW)); old_prio =3D p->prio; p->prio =3D effective_prio(p); =20 @@ -7212,7 +7212,7 @@ 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, !(READ_ONCE(p->__state) & TASK_NEW)); } =20 /* --=20 2.34.1