From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752192AbdCPNAV (ORCPT ); Thu, 16 Mar 2017 09:00:21 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:38465 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752155AbdCPNAS (ORCPT ); Thu, 16 Mar 2017 09:00:18 -0400 Message-Id: <20170316125823.140295131@infradead.org> User-Agent: quilt/0.63-1 Date: Thu, 16 Mar 2017 13:47:48 +0100 From: Peter Zijlstra To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, acme@kernel.org, mathieu.desnoyers@efficios.com, alexander.shishkin@linux.intel.com, dvyukov@google.com, fweisbec@gmail.com, oleg@redhat.com, peterz@infradead.org, stable@vger.kernel.org Subject: [PATCH 1/4] perf: Fix use-after-free in perf_release() References: <20170316124747.804596354@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-perf-UAF-perf_release.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Cc: Arnaldo Carvalho de Melo Cc: Mathieu Desnoyers Cc: Ingo Molnar Cc: Alexander Shishkin Cc: stable@vger.kernel.org Fixes: c6e5b73242d2 ("perf: Synchronously clean up child events") Reported-by: Dmitry Vyukov Spotted-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/20170314155949.GE32474@worktop --- kernel/events/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10556,6 +10556,17 @@ 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)