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=-23.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,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 5F468C43460 for ; Mon, 5 Apr 2021 08:57:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 404CB6139C for ; Mon, 5 Apr 2021 08:57:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233068AbhDEI5H (ORCPT ); Mon, 5 Apr 2021 04:57:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:35640 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232950AbhDEI4y (ORCPT ); Mon, 5 Apr 2021 04:56:54 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4293861394; Mon, 5 Apr 2021 08:56:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1617613008; bh=4eVUD4Yn1dwPr0iZwZB5iNy4j2G3UwM1o9+BIme31k8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YxunZLdQBEX9dJn8ihN+GDJ77cAzaniw2MwSH3po8AGbQ5WnY+VX5sES4k59OguBB SRD6ycPW9ehUOucc/Hh54EFGDiCH91qGKlC+2ZMay19R4G3VGRKpnQgoFDsLKSGJJj evehlREPo2txCEChuwnBDpazxyro+zPqgRSz6P24= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jesper Dangaard Brouer , Daniel Borkmann , John Fastabend Subject: [PATCH 4.9 18/35] bpf: Remove MTU check in __bpf_skb_max_len Date: Mon, 5 Apr 2021 10:53:53 +0200 Message-Id: <20210405085019.455875111@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210405085018.871387942@linuxfoundation.org> References: <20210405085018.871387942@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: Jesper Dangaard Brouer commit 6306c1189e77a513bf02720450bb43bd4ba5d8ae upstream. Multiple BPF-helpers that can manipulate/increase the size of the SKB uses __bpf_skb_max_len() as the max-length. This function limit size against the current net_device MTU (skb->dev->mtu). When a BPF-prog grow the packet size, then it should not be limited to the MTU. The MTU is a transmit limitation, and software receiving this packet should be allowed to increase the size. Further more, current MTU check in __bpf_skb_max_len uses the MTU from ingress/current net_device, which in case of redirects uses the wrong net_device. This patch keeps a sanity max limit of SKB_MAX_ALLOC (16KiB). The real limit is elsewhere in the system. Jesper's testing[1] showed it was not possible to exceed 8KiB when expanding the SKB size via BPF-helper. The limiting factor is the define KMALLOC_MAX_CACHE_SIZE which is 8192 for SLUB-allocator (CONFIG_SLUB) in-case PAGE_SIZE is 4096. This define is in-effect due to this being called from softirq context see code __gfp_pfmemalloc_flags() and __do_kmalloc_node(). Jakub's testing showed that frames above 16KiB can cause NICs to reset (but not crash). Keep this sanity limit at this level as memory layer can differ based on kernel config. [1] https://github.com/xdp-project/bpf-examples/tree/master/MTU-tests Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Daniel Borkmann Acked-by: John Fastabend Link: https://lore.kernel.org/bpf/161287788936.790810.2937823995775097177.stgit@firesoul Signed-off-by: Greg Kroah-Hartman --- net/core/filter.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2120,10 +2120,7 @@ static u32 __bpf_skb_min_len(const struc return min_len; } -static u32 __bpf_skb_max_len(const struct sk_buff *skb) -{ - return skb->dev->mtu + skb->dev->hard_header_len; -} +#define BPF_SKB_MAX_LEN SKB_MAX_ALLOC static int bpf_skb_grow_rcsum(struct sk_buff *skb, unsigned int new_len) { @@ -2144,7 +2141,7 @@ static int bpf_skb_trim_rcsum(struct sk_ BPF_CALL_3(bpf_skb_change_tail, struct sk_buff *, skb, u32, new_len, u64, flags) { - u32 max_len = __bpf_skb_max_len(skb); + u32 max_len = BPF_SKB_MAX_LEN; u32 min_len = __bpf_skb_min_len(skb); int ret;