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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E519DC433F5 for ; Thu, 27 Jan 2022 20:57:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245203AbiA0U5C (ORCPT ); Thu, 27 Jan 2022 15:57:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245158AbiA0U5B (ORCPT ); Thu, 27 Jan 2022 15:57:01 -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 6F768C061714 for ; Thu, 27 Jan 2022 12:57:01 -0800 (PST) Received: by mail-pf1-x429.google.com with SMTP id v74so3961134pfc.1 for ; Thu, 27 Jan 2022 12:57:01 -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:in-reply-to:references :mime-version:content-transfer-encoding; bh=tfXY+yoEkXRjHsPlcj+EE4YfwHLvMltbNM3WmPepjHA=; b=ViP7LO+i4/X8Hza5L1TLV+4t5dn6LsbwwzM+xuF427VZ6hm3nM7jfWCKefjh/+qRTM th0se3ZeJw+d25HTdz0fNd3X4YSWfmfU8XGrU/ru6srSikqzmOuSsbJGU1ZFwyThntYQ TsEJLBtNw151HP+s+5wwC8cvBJw+DXaYIMKYW1BSLHa0zkxLBacK0LkumsvGcjj7l/TU AUpREyLthSnm4F9S0ig/wBzlDRutKae1aZcHVWdW+XL0SJrbQ52Y7TZ5ChmVr6F4yZH3 0l4JNZmDqOwjvCppwxH/5b7lOv64dT81vAORBp1kjkP8td+S8uQh28xNhlBZa6n/ru1O m92w== 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=tfXY+yoEkXRjHsPlcj+EE4YfwHLvMltbNM3WmPepjHA=; b=L04B6eJS3AkSv+Gfm1Or+e+vC4X7SG+rS4HRVS69uU8+SVNytEiAFIb/WDeBsCGQp9 dvK9XrjdxHkbgynfttwrU78Cx5tBblEhkmFJxLv+xRhmPfADofRyNpZCVSq/LxRvoxNF vkun++9vTyessTlaz5jMX/DhCTkK8e1vd9jsDJqm27Igsj2FR6Tb98n2JSaZG3AfS+bx AMMCHsaMN6FBD9nGVt3NJPnDyFr1+NYxCpkU2wb9hpcZzU3Qwypg+wiOK3w6bQ2c5HGM DDgEwKBxN0yfqg+3aykCg+LwPZIgDXEZxLNPDEmhvWDfE/JJhtUszMTbS2WWxPNAyeZD jCsQ== X-Gm-Message-State: AOAM533kvwfsGediwRYHYVEO3hrahyh5qYX7dx+WnThFBDoKoK43YS6d xiPZ1KL41txwUFQDH2e3czX52g== X-Google-Smtp-Source: ABdhPJzjNYJyU2lRmm2ARtHfs1fz4x84l4Mv3pZVcHntWHtR8Cec3OXniogqV4YqFbiWauRmgfssHQ== X-Received: by 2002:a62:3042:: with SMTP id w63mr4562471pfw.71.1643317020815; Thu, 27 Jan 2022 12:57:00 -0800 (PST) Received: from localhost.localdomain ([50.39.160.154]) by smtp.gmail.com with ESMTPSA id nv13sm216748pjb.18.2022.01.27.12.57.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jan 2022 12:57:00 -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 , stable@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Subject: [PATCH v4] sched/fair: Fix fault in reweight_entity Date: Thu, 27 Jan 2022 12:56:23 -0800 Message-Id: <20220127205623.1258029-1-tadeusz.struk@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220125193403.778497-1-tadeusz.struk@linaro.org> References: <20220125193403.778497-1-tadeusz.struk@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@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 is a race between sched_post_fork() and setpriority(PRIO_PGRP) within a thread group that causes a null-ptr-deref in 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(), as it will try to access the run queue pointer, which 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 04/01/2014 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 ---[ 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 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. 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: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org Link: https://syzkaller.appspot.com/bug?id=9d9c27adc674e3a7932b22b61c79a02da82cbdc1 Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group") Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk --- Changes in v4: - Removed the update_load param from set_load_weight() and call reweight_task() based on the TASK_NEW flag Changes in v3: - Removed the new check and changed the update_load condition from always true to true if p->state != TASK_NEW Changes in v2: - Added a check in set_user_nice(), and return from there if the task is not fully setup instead of returning from reweight_entity() --- kernel/sched/core.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 848eaa0efe0e..a0ef4670e695 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1214,10 +1214,12 @@ int tg_nop(struct task_group *tg, void *data) } #endif -static void set_load_weight(struct task_struct *p, bool update_load) +static void set_load_weight(struct task_struct *p) { int prio = p->static_prio - MAX_RT_PRIO; struct load_weight *load = &p->se.load; + bool update_load = !(READ_ONCE(p->__state) & TASK_NEW); + /* * SCHED_IDLE tasks get minimal weight: @@ -4406,7 +4408,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) p->static_prio = NICE_TO_PRIO(0); p->prio = p->normal_prio = p->static_prio; - set_load_weight(p, false); + set_load_weight(p); /* * We don't need the reset flag anymore after the fork. It has @@ -6921,7 +6923,7 @@ void set_user_nice(struct task_struct *p, long nice) put_prev_task(rq, p); p->static_prio = NICE_TO_PRIO(nice); - set_load_weight(p, true); + set_load_weight(p); old_prio = p->prio; p->prio = effective_prio(p); @@ -7212,7 +7214,7 @@ static void __setscheduler_params(struct task_struct *p, */ p->rt_priority = attr->sched_priority; p->normal_prio = normal_prio(p); - set_load_weight(p, true); + set_load_weight(p); } /* @@ -9445,7 +9447,7 @@ void __init sched_init(void) #endif } - set_load_weight(&init_task, false); + set_load_weight(&init_task); /* * The boot idle thread does lazy MMU switching as well: -- 2.34.1