From patchwork Sun Jun 18 20:50:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: tip-bot2 for Thomas Gleixner X-Patchwork-Id: 109670 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp2636460vqr; Sun, 18 Jun 2023 13:58:26 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ4SW7MT0qG1JFESi3dq1+JykAdmGTQxPPIHmSkF81jCGvQJFNE6XA5q9mvTegKBD6R8mY0H X-Received: by 2002:a92:c70f:0:b0:33e:5ea2:bd00 with SMTP id a15-20020a92c70f000000b0033e5ea2bd00mr288765ilp.17.1687121906282; Sun, 18 Jun 2023 13:58:26 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1687121906; cv=none; d=google.com; s=arc-20160816; b=I9J9cUZVzREtDD4k4PfIByC/+TZoJdfsLJtZnDTStD1VD/7sN0fZmhtTrXI0CNq63+ y1vOfSQGaZlUwlv6/5FtPT5kbDOjX1w2JiJ96aI82LVCMoCWn80kBCC6cH/wqShHZ09h 2naaHiLO3FKaB+wjQtyhhOjaQbVfTM4SuPW6OUBHk3jN7scgSvi4aknbrZ5E8BDxugf9 xP6K9L5vFNDk7NoNVLbBpjuSen4IZSUSRU3QZveamY6qJxctVOj1OTP7X/uExW6SqPJK N7K+oOIskOpbL0PDV6k/N5iq2No37Ms/R+qRgta11YgTVczxtUKXASI/HHODESPcocqr VdUw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:robot-unsubscribe :robot-id:message-id:mime-version:references:in-reply-to:cc:subject :to:reply-to:sender:from:dkim-signature:dkim-signature:date; bh=/F4iP9SdBXFdAGaxPkH5ta1aHllR3vAjqy9jhfMl7yA=; b=QOtcL/yFSKuIJXH03q35CUidVDqCDF/eOqZhtTkHwRGSHeTJwKT3aO2uR6Dfaq56R/ JxzlnmZD3hOs4e8ytfxsLgIpoJOqoZFeM7xdeOvnl7SKIae9eJXw8WKG7rNa7JQuDBNL LpkmFr7Q8aJb9uU6/UudOS5Bu2YpQRCtPUL+H6ABXHB5wlC+SQaNzEgx7N0EweJkw/cl emTQaTYeQZTmJWNW/+EPuppvSKCGbtMe3NW9j/UNMTIrAmprW6Xf0O/vWrQjPoXScti5 O178tNhvnqmznqMCJI4J+Ttde2CzcnqZT6i1DFsqbjEDFF6aiYYhhg3/38kuc1WGplBg +2UA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=eqCgSnUF; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e header.b=DCUg6kqv; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id x11-20020a170902820b00b001b3d822f131si12727030pln.239.2023.06.18.13.58.14; Sun, 18 Jun 2023 13:58:26 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=eqCgSnUF; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e header.b=DCUg6kqv; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229761AbjFRUvO (ORCPT + 99 others); Sun, 18 Jun 2023 16:51:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229675AbjFRUuO (ORCPT ); Sun, 18 Jun 2023 16:50:14 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4CF5DE5F; Sun, 18 Jun 2023 13:50:10 -0700 (PDT) Date: Sun, 18 Jun 2023 20:50:08 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1687121408; 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=/F4iP9SdBXFdAGaxPkH5ta1aHllR3vAjqy9jhfMl7yA=; b=eqCgSnUFockrGcvAA9QICTVbcf+PjQvbHnmpnYSAR8MhUN2HW7TtSQWIAK479YOQZTOyAt j5sie1NczNUOia3SjW9EGjxQ+qnueeJ1QjhH6mgOnC4NNcTF/mFkOPRz29tn+XCODEUWzY WBxcnL862PSxmIujvD9mohGUropujP9qNMR/D/OHX6RNg6CuB/Hl2VQ+q6DEKc9cXebjEg r3GvNgj4ouPUYKkOjOWJOsRzA+tYnjLao0ZjUfBVR2B1VNiNglfCgyFr+hXqDZq8KJ7kTX 0e9GjXOzwsQzBsitsItQ5JIz9Mx6B03jMvd3KvGC2+Q5ePDjhxzgjHBPLnwLCA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1687121408; 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=/F4iP9SdBXFdAGaxPkH5ta1aHllR3vAjqy9jhfMl7yA=; b=DCUg6kqvO2Wve893ELypLdCVtxq52bYP94xjvfrwMTDls6YFIDw+mXBzOxgI1uQNiuuZ3y d/onRb327kCQP1AA== From: "tip-bot2 for Thomas Gleixner" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] posix-timers: Ensure timer ID search-loop limit is valid Cc: syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com, Dmitry Vyukov , Thomas Gleixner , Frederic Weisbecker , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <87bkhzdn6g.ffs@tglx> References: <87bkhzdn6g.ffs@tglx> MIME-Version: 1.0 Message-ID: <168712140837.404.7747591826658395670.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1764176368182784315?= X-GMAIL-MSGID: =?utf-8?q?1769075540162627151?= The following commit has been merged into the timers/core branch of tip: Commit-ID: 8ce8849dd1e78dadcee0ec9acbd259d239b7069f Gitweb: https://git.kernel.org/tip/8ce8849dd1e78dadcee0ec9acbd259d239b7069f Author: Thomas Gleixner AuthorDate: Thu, 01 Jun 2023 20:58:47 +02:00 Committer: Thomas Gleixner CommitterDate: Sun, 18 Jun 2023 22:41:48 +02:00 posix-timers: Ensure timer ID search-loop limit is valid posix_timer_add() tries to allocate a posix timer ID by starting from the cached ID which was stored by the last successful allocation. This is done in a loop searching the ID space for a free slot one by one. The loop has to terminate when the search wrapped around to the starting point. But that's racy vs. establishing the starting point. That is read out lockless, which leads to the following problem: CPU0 CPU1 posix_timer_add() start = sig->posix_timer_id; lock(hash_lock); ... posix_timer_add() if (++sig->posix_timer_id < 0) start = sig->posix_timer_id; sig->posix_timer_id = 0; So CPU1 can observe a negative start value, i.e. -1, and the loop break never happens because the condition can never be true: if (sig->posix_timer_id == start) break; While this is unlikely to ever turn into an endless loop as the ID space is huge (INT_MAX), the racy read of the start value caught the attention of KCSAN and Dmitry unearthed that incorrectness. Rewrite it so that all id operations are under the hash lock. Reported-by: syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com Reported-by: Dmitry Vyukov Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lore.kernel.org/r/87bkhzdn6g.ffs@tglx --- include/linux/sched/signal.h | 2 +- kernel/time/posix-timers.c | 31 ++++++++++++++++++------------- 2 files changed, 19 insertions(+), 14 deletions(-) diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 2009926..669e8cf 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -135,7 +135,7 @@ struct signal_struct { #ifdef CONFIG_POSIX_TIMERS /* POSIX.1b Interval Timers */ - int posix_timer_id; + unsigned int next_posix_timer_id; struct list_head posix_timers; /* ITIMER_REAL timer for the process */ diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index ed3c4a9..2d6cf93 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -140,25 +140,30 @@ static struct k_itimer *posix_timer_by_id(timer_t id) static int posix_timer_add(struct k_itimer *timer) { struct signal_struct *sig = current->signal; - int first_free_id = sig->posix_timer_id; struct hlist_head *head; - int ret = -ENOENT; + unsigned int cnt, id; - do { + /* + * FIXME: Replace this by a per signal struct xarray once there is + * a plan to handle the resulting CRIU regression gracefully. + */ + for (cnt = 0; cnt <= INT_MAX; cnt++) { spin_lock(&hash_lock); - head = &posix_timers_hashtable[hash(sig, sig->posix_timer_id)]; - if (!__posix_timers_find(head, sig, sig->posix_timer_id)) { + id = sig->next_posix_timer_id; + + /* Write the next ID back. Clamp it to the positive space */ + sig->next_posix_timer_id = (id + 1) & INT_MAX; + + head = &posix_timers_hashtable[hash(sig, id)]; + if (!__posix_timers_find(head, sig, id)) { hlist_add_head_rcu(&timer->t_hash, head); - ret = sig->posix_timer_id; + spin_unlock(&hash_lock); + return id; } - if (++sig->posix_timer_id < 0) - sig->posix_timer_id = 0; - if ((sig->posix_timer_id == first_free_id) && (ret == -ENOENT)) - /* Loop over all possible ids completed */ - ret = -EAGAIN; spin_unlock(&hash_lock); - } while (ret == -ENOENT); - return ret; + } + /* POSIX return code when no timer ID could be allocated */ + return -EAGAIN; } static inline void unlock_timer(struct k_itimer *timr, unsigned long flags)