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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT 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 B9B29C4360F for ; Tue, 12 Mar 2019 18:03:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8BCB12177E for ; Tue, 12 Mar 2019 18:03:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552413792; bh=a0oytfARmBA8nk8UsHsNzcvQ3W99CX4ejXRxtke/j7Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=rRxlmPKIuCzsAjTNxXx547HRHdSvju8dn6eyaccggMsHBj0jaOc5RBDr2y4fP2h8O +loS/7Ah9tcQ78guj8jrvdy8wGISE3wG6hZ1almMOgOOmDYk2Ayrs/9xaE+KPQD6QG hob9hte6HIHApRtFr2gmHUwkVqHCD9T5P+K8yoYQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728171AbfCLSDL (ORCPT ); Tue, 12 Mar 2019 14:03:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:48978 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727707AbfCLRM4 (ORCPT ); Tue, 12 Mar 2019 13:12:56 -0400 Received: from localhost (unknown [104.133.8.98]) (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 BCEFC217F4; Tue, 12 Mar 2019 17:12:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552410775; bh=a0oytfARmBA8nk8UsHsNzcvQ3W99CX4ejXRxtke/j7Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ziPcqWAkzHHdDsBM1Ce/w3CelkhoVZCH40OtXSJOgpn5ULtJ1goIt5xcWqy3Om6Uj Yw6AZfIeJoveWhXJ4m32SX3x3gDsYl4TWST+sQNfZonz/MQnyEVNNKM/kyZGR/plg4 j8rdKzVos1HhTKfvpYlaNCYDFGigKBqwALrGg99o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , Alexei Starovoitov , Martin KaFai Lau , Daniel Borkmann , Sasha Levin Subject: [PATCH 4.20 114/171] bpf: Fix syscalls stackmap lookup potential deadlock Date: Tue, 12 Mar 2019 10:08:14 -0700 Message-Id: <20190312170357.712585962@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190312170347.868927101@linuxfoundation.org> References: <20190312170347.868927101@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 7c4cd051add3d00bbff008a133c936c515eaa8fe ] The map_lookup_elem used to not acquiring spinlock in order to optimize the reader. It was true until commit 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation") The syscall's map_lookup_elem(stackmap) calls bpf_stackmap_copy(). bpf_stackmap_copy() may find the elem no longer needed after the copy is done. If that is the case, pcpu_freelist_push() saves this elem for reuse later. This push requires a spinlock. If a tracing bpf_prog got run in the middle of the syscall's map_lookup_elem(stackmap) and this tracing bpf_prog is calling bpf_get_stackid(stackmap) which also requires the same pcpu_freelist's spinlock, it may end up with a dead lock situation as reported by Eric Dumazet in https://patchwork.ozlabs.org/patch/1030266/ The situation is the same as the syscall's map_update_elem() which needs to acquire the pcpu_freelist's spinlock and could race with tracing bpf_prog. Hence, this patch fixes it by protecting bpf_stackmap_copy() with this_cpu_inc(bpf_prog_active) to prevent tracing bpf_prog from running. A later syscall's map_lookup_elem commit f1a2e44a3aec ("bpf: add queue and stack maps") also acquires a spinlock and races with tracing bpf_prog similarly. Hence, this patch is forward looking and protects the majority of the map lookups. bpf_map_offload_lookup_elem() is the exception since it is for network bpf_prog only (i.e. never called by tracing bpf_prog). Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation") Reported-by: Eric Dumazet Acked-by: Alexei Starovoitov Signed-off-by: Martin KaFai Lau Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Signed-off-by: Sasha Levin --- kernel/bpf/syscall.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index cf5040fd5434..5f03ddf7b615 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -712,8 +712,13 @@ static int map_lookup_elem(union bpf_attr *attr) if (bpf_map_is_dev_bound(map)) { err = bpf_map_offload_lookup_elem(map, key, value); - } else if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH || - map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) { + goto done; + } + + preempt_disable(); + this_cpu_inc(bpf_prog_active); + if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH || + map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) { err = bpf_percpu_hash_copy(map, key, value); } else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) { err = bpf_percpu_array_copy(map, key, value); @@ -743,7 +748,10 @@ static int map_lookup_elem(union bpf_attr *attr) } rcu_read_unlock(); } + this_cpu_dec(bpf_prog_active); + preempt_enable(); +done: if (err) goto free_value; -- 2.19.1