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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 A822AC64E7D for ; Tue, 17 Nov 2020 13:13:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52C7124199 for ; Tue, 17 Nov 2020 13:13:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="lMF2PnXU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729923AbgKQNNL (ORCPT ); Tue, 17 Nov 2020 08:13:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:43450 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728827AbgKQNNG (ORCPT ); Tue, 17 Nov 2020 08:13:06 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DE78C221EB; Tue, 17 Nov 2020 13:13:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605618786; bh=7VGnJb/e2JX3WsNJAqASnGnKnnUvJYAr5ZezzCKHD/E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lMF2PnXUHSSLwKP0heeixyArmfjzaygeBJDmebp6h6uMKmkIcmeL6164nSIhit2hT sVCqIRV9LGkE+PeFA0NsYN6rdkn+Ux3m7lyOCrmeVZ67knx9ZE2p8UHCqW0NmDicKt hQ884Ck0W89+KdGP8yfixVjA8EUWvWom+zWrHQtY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Michael Petlan , Jiri Olsa , Ingo Molnar , Peter Zijlstra , Namhyung Kim , Wade Mealing , Sudip Mukherjee Subject: [PATCH 4.9 74/78] perf/core: Fix race in the perf_mmap_close() function Date: Tue, 17 Nov 2020 14:05:40 +0100 Message-Id: <20201117122112.722605910@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201117122109.116890262@linuxfoundation.org> References: <20201117122109.116890262@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jiri Olsa commit f91072ed1b7283b13ca57fcfbece5a3b92726143 upstream. There's a possible race in perf_mmap_close() when checking ring buffer's mmap_count refcount value. The problem is that the mmap_count check is not atomic because we call atomic_dec() and atomic_read() separately. perf_mmap_close: ... atomic_dec(&rb->mmap_count); ... if (atomic_read(&rb->mmap_count)) goto out_put; free_uid out_put: ring_buffer_put(rb); /* could be last */ The race can happen when we have two (or more) events sharing same ring buffer and they go through atomic_dec() and then they both see 0 as refcount value later in atomic_read(). Then both will go on and execute code which is meant to be run just once. The code that detaches ring buffer is probably fine to be executed more than once, but the problem is in calling free_uid(), which will later on demonstrate in related crashes and refcount warnings, like: refcount_t: addition on 0; use-after-free. ... RIP: 0010:refcount_warn_saturate+0x6d/0xf ... Call Trace: prepare_creds+0x190/0x1e0 copy_creds+0x35/0x172 copy_process+0x471/0x1a80 _do_fork+0x83/0x3a0 __do_sys_wait4+0x83/0x90 __do_sys_clone+0x85/0xa0 do_syscall_64+0x5b/0x1e0 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Using atomic decrease and check instead of separated calls. Tested-by: Michael Petlan Signed-off-by: Jiri Olsa Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Namhyung Kim Acked-by: Wade Mealing Fixes: 9bb5d40cd93c ("perf: Fix mmap() accounting hole"); Link: https://lore.kernel.org/r/20200916115311.GE2301783@krava [sudip: backport to v4.9.y by using ring_buffer] Signed-off-by: Sudip Mukherjee Signed-off-by: Greg Kroah-Hartman --- kernel/events/core.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5069,11 +5069,11 @@ static void perf_pmu_output_stop(struct static void perf_mmap_close(struct vm_area_struct *vma) { struct perf_event *event = vma->vm_file->private_data; - struct ring_buffer *rb = ring_buffer_get(event); struct user_struct *mmap_user = rb->mmap_user; int mmap_locked = rb->mmap_locked; unsigned long size = perf_data_size(rb); + bool detach_rest = false; if (event->pmu->event_unmapped) event->pmu->event_unmapped(event); @@ -5104,7 +5104,8 @@ static void perf_mmap_close(struct vm_ar mutex_unlock(&event->mmap_mutex); } - atomic_dec(&rb->mmap_count); + if (atomic_dec_and_test(&rb->mmap_count)) + detach_rest = true; if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) goto out_put; @@ -5113,7 +5114,7 @@ static void perf_mmap_close(struct vm_ar mutex_unlock(&event->mmap_mutex); /* If there's still other mmap()s of this buffer, we're done. */ - if (atomic_read(&rb->mmap_count)) + if (!detach_rest) goto out_put; /*