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 X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58AD1C48BD4 for ; Tue, 25 Jun 2019 10:43:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20B2D20663 for ; Tue, 25 Jun 2019 10:43:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="tNpuKDID" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729095AbfFYKnr (ORCPT ); Tue, 25 Jun 2019 06:43:47 -0400 Received: from merlin.infradead.org ([205.233.59.134]:56586 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbfFYKnr (ORCPT ); Tue, 25 Jun 2019 06:43:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=bX0AUbriIdW8uB8m351hBABxw7tgECbO9YEwMIEHwrQ=; b=tNpuKDIDuUrSdoDiaPT/u2qdB 50hIvL2r50PbwNs1jQ99TRYSifU64HfISbwd29t+N4skDcrjviu9F4q2/0lGv2FPRSx1GHSPas/Me fgYZRFqB3IPcvw005nt0DHzQQ2g4E8gKPGUlQlHWT2fVuF8bqCCFARuqg06YHn3FizgTeW4+qtW3t uqxvNfljvOS+ayaHEPGfXgns0zb9ll+ThJxWjm/tx5tuqJfMRVXVYnvkABwYsXvtlaD2AmjdUECJL obZpiDUBQMW4uG/XtxD/DyyAVJyBKnhKX9vnL4HIMIBpZE9K15AFts80KqnswHQ8TVCD/lDE32JO5 CCeB9zsFQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hfiv4-0006iT-NO; Tue, 25 Jun 2019 10:43:23 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 5FEAB20A0643C; Tue, 25 Jun 2019 12:43:20 +0200 (CEST) Date: Tue, 25 Jun 2019 12:43:20 +0200 From: Peter Zijlstra To: Mark Rutland Cc: Alexander Shishkin , Arnaldo Carvalho de Melo , Ingo Molnar , linux-kernel@vger.kernel.org, jolsa@redhat.com, dvyukov@google.com, namhyung@kernel.org, xiexiuqi@huawei.com, syzbot+a24c397a29ad22d86c98@syzkaller.appspotmail.com Subject: [PATCH] perf: Fix race between close() and fork() Message-ID: <20190625104320.GZ3463@hirez.programming.kicks-ass.net> References: <278ac311-d8f3-2832-5fa1-522471c8c31c@huawei.com> <20190228140109.64238-1-alexander.shishkin@linux.intel.com> <20190308155429.GB10860@lakrids.cambridge.arm.com> <20190624121902.GE3436@hirez.programming.kicks-ass.net> <20190625084904.GY3463@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190625084904.GY3463@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Syzcaller reported the following Use-after-Free issue: close() clone() copy_process() perf_event_init_task() perf_event_init_context() mutex_lock(parent_ctx->mutex) inherit_task_group() inherit_group() inherit_event() mutex_lock(event->child_mutex) // expose event on child list list_add_tail() mutex_unlock(event->child_mutex) mutex_unlock(parent_ctx->mutex) ... goto bad_fork_* bad_fork_cleanup_perf: perf_event_free_task() perf_release() perf_event_release_kernel() list_for_each_entry() mutex_lock(ctx->mutex) mutex_lock(event->child_mutex) // event is from the failing inherit // on the other CPU perf_remove_from_context() list_move() mutex_unlock(event->child_mutex) mutex_unlock(ctx->mutex) mutex_lock(ctx->mutex) list_for_each_entry_safe() // event already stolen mutex_unlock(ctx->mutex) delayed_free_task() free_task() list_for_each_entry_safe() list_del() free_event() _free_event() // and so event->hw.target // is the already freed failed clone() if (event->hw.target) put_task_struct(event->hw.target) // WHOOPSIE, already quite dead Which puts the lie to the the comment on perf_event_free_task(): 'unexposed, unused context' not so much. Which is a 'fun' confluence of fail; copy_process() doing an unconditional free_task() and not respecting refcounts, and perf having creative locking. In particular: 82d94856fa22 ("perf/core: Fix lock inversion between perf,trace,cpuhp") seems to have overlooked this 'fun' parade. Solve it by using the fact that detached events still have a reference count on their (previous) context. With this perf_event_free_task() can detect when events have escaped and wait for their destruction. Cc: Mark Rutland Fixes: 82d94856fa22 ("perf/core: Fix lock inversion between perf,trace,cpuhp") Reported-by: syzbot+a24c397a29ad22d86c98@syzkaller.appspotmail.com Debugged-by: Alexander Shishkin Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/core.c | 49 +++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 41 insertions(+), 8 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 10c1dba9068c..5302c19e9892 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4463,12 +4463,20 @@ static void _free_event(struct perf_event *event) if (event->destroy) event->destroy(event); - if (event->ctx) - put_ctx(event->ctx); - + /* + * Must be after ->destroy(), due to uprobe_perf_close() using + * hw.target. + */ if (event->hw.target) put_task_struct(event->hw.target); + /* + * perf_event_free_task() relies on put_ctx() being 'last', in particular + * all task references must be cleaned up. + */ + if (event->ctx) + put_ctx(event->ctx); + exclusive_event_destroy(event); module_put(event->pmu->module); @@ -4648,8 +4656,17 @@ int perf_event_release_kernel(struct perf_event *event) mutex_unlock(&event->child_mutex); list_for_each_entry_safe(child, tmp, &free_list, child_list) { + void *var = &child->ctx->refcount; + list_del(&child->child_list); free_event(child); + + /* + * Wake any perf_event_free_task() waiting for this event to be + * freed. + */ + smp_mb(); /* pairs with wait_var_event() */ + wake_up_var(var); } no_ctx: @@ -11512,11 +11529,11 @@ static void perf_free_event(struct perf_event *event, } /* - * Free an unexposed, unused context as created by inheritance by - * perf_event_init_task below, used by fork() in case of fail. + * Free a context as created by inheritance by perf_event_init_task() below, + * used by fork() in case of fail. * - * Not all locks are strictly required, but take them anyway to be nice and - * help out with the lockdep assertions. + * Even though the task has never lived, the context and events have been + * exposed through the child_list, so we must take care tearing it all down. */ void perf_event_free_task(struct task_struct *task) { @@ -11546,7 +11563,23 @@ void perf_event_free_task(struct task_struct *task) perf_free_event(event, ctx); mutex_unlock(&ctx->mutex); - put_ctx(ctx); + + /* + * perf_event_release_kernel() could've stolen some of our + * child events and still have them on its free_list. In that + * case we must wait for these events to have been freed (in + * particular all their references to this task must've been + * dropped). + * + * Without this copy_process() will unconditionally free this + * task (irrespective of its reference count) and + * _free_event()'s put_task_struct(event->hw.target) will be a + * use-after-free. + * + * Wait for all events to drop their context reference. + */ + wait_var_event(&ctx->refcount, refcount_read(&ctx->refcount) == 1); + put_ctx(ctx); /* must be last */ } }