From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935172AbdCXSJV (ORCPT ); Fri, 24 Mar 2017 14:09:21 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37352 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755181AbdCXSHG (ORCPT ); Fri, 24 Mar 2017 14:07:06 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dmitry Vyukov , "Peter Zijlstra (Intel)" , Alexander Shishkin , Arnaldo Carvalho de Melo , Arnaldo Carvalho de Melo , Jiri Olsa , Linus Torvalds , Mathieu Desnoyers , Stephane Eranian , Thomas Gleixner , Vince Weaver , fweisbec@gmail.com, oleg@redhat.com, Ingo Molnar Subject: [PATCH 4.10 07/27] perf/core: Fix use-after-free in perf_release() Date: Fri, 24 Mar 2017 18:58:25 +0100 Message-Id: <20170324151226.516586576@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170324151225.973768798@linuxfoundation.org> References: <20170324151225.973768798@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra commit e552a8389aa409e257b7dcba74f67f128f979ccc upstream. Dmitry reported syzcaller tripped a use-after-free in perf_release(). After much puzzlement Oleg spotted the below scenario: Task1 Task2 fork() perf_event_init_task() /* ... */ goto bad_fork_$foo; /* ... */ perf_event_free_task() mutex_lock(ctx->lock) perf_free_event(B) perf_event_release_kernel(A) mutex_lock(A->child_mutex) list_for_each_entry(child, ...) { /* child == B */ ctx = B->ctx; get_ctx(ctx); mutex_unlock(A->child_mutex); mutex_lock(A->child_mutex) list_del_init(B->child_list) mutex_unlock(A->child_mutex) /* ... */ mutex_unlock(ctx->lock); put_ctx() /* >0 */ free_task(); mutex_lock(ctx->lock); mutex_lock(A->child_mutex); /* ... */ mutex_unlock(A->child_mutex); mutex_unlock(ctx->lock) put_ctx() /* 0 */ ctx->task && !TOMBSTONE put_task_struct() /* UAF */ This patch closes the hole by making perf_event_free_task() destroy the task <-> ctx relation such that perf_event_release_kernel() will no longer observe the now dead task. Spotted-by: Oleg Nesterov Reported-by: Dmitry Vyukov Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Mathieu Desnoyers Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: fweisbec@gmail.com Cc: oleg@redhat.com Fixes: c6e5b73242d2 ("perf: Synchronously clean up child events") Link: http://lkml.kernel.org/r/20170314155949.GE32474@worktop Link: http://lkml.kernel.org/r/20170316125823.140295131@infradead.org Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/events/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10374,6 +10374,17 @@ void perf_event_free_task(struct task_st continue; mutex_lock(&ctx->mutex); + raw_spin_lock_irq(&ctx->lock); + /* + * Destroy the task <-> ctx relation and mark the context dead. + * + * This is important because even though the task hasn't been + * exposed yet the context has been (through child_list). + */ + RCU_INIT_POINTER(task->perf_event_ctxp[ctxn], NULL); + WRITE_ONCE(ctx->task, TASK_TOMBSTONE); + put_task_struct(task); /* cannot be last */ + raw_spin_unlock_irq(&ctx->lock); again: list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)