Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A168AC433FE for ; Wed, 24 Nov 2021 12:31:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343650AbhKXMed (ORCPT ); Wed, 24 Nov 2021 07:34:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:42282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244323AbhKXM1D (ORCPT ); Wed, 24 Nov 2021 07:27:03 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id DC6E061241; Wed, 24 Nov 2021 12:16:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1637756194; bh=1BVPdN4QLiMMBKH9SxvscAvHKv04yir39+uRLmntIwQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aNDg4KSn7QUAzJ8Fe2AZOFK2zVHuKvPdDZnxj6MecGREagMFdHCHNOAzTCvOwEW8q iyIGvTew9XMZd4Uo/lvuEFYTlZ6mZUqiYylr8ACh5cHSfXyOUTckFXy6K4hzMubDSW Nz6OoMCSqId5zMYjPEky4vn0gY0lwfc0IYpfv7fo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Martin Weinelt , Sven Eckelmann , =?UTF-8?q?Linus=20L=FCssing?= , Simon Wunderlich Subject: [PATCH 4.9 198/207] batman-adv: Keep fragments equally sized Date: Wed, 24 Nov 2021 12:57:49 +0100 Message-Id: <20211124115710.358366672@linuxfoundation.org> X-Mailer: git-send-email 2.34.0 In-Reply-To: <20211124115703.941380739@linuxfoundation.org> References: <20211124115703.941380739@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: Sven Eckelmann commit 1c2bcc766be44467809f1798cd4ceacafe20a852 upstream. The batman-adv fragmentation packets have the design problem that they cannot be refragmented and cannot handle padding by the underlying link. The latter often leads to problems when networks are incorrectly configured and don't use a common MTU. The sender could for example fragment a 1271 byte frame (plus external ethernet header (14) and batadv unicast header (10)) to fit in a 1280 bytes large MTU of the underlying link (max. 1294 byte frames). This would create a 1294 bytes large frame (fragment 2) and a 55 bytes large frame (fragment 1). The extra 54 bytes are the fragment header (20) added to each fragment and the external ethernet header (14) for the second fragment. Let us assume that the next hop is then not able to transport 1294 bytes to its next hop. The 1294 byte large frame will be dropped but the 55 bytes large fragment will still be forwarded to its destination. Or let us assume that the underlying hardware requires that each frame has a minimum size (e.g. 60 bytes). Then it will pad the 55 bytes frame to 60 bytes. The receiver of the 60 bytes frame will no longer be able to correctly assemble the two frames together because it is not aware that 5 bytes of the 60 bytes frame are padding and don't belong to the reassembled frame. This can partly be avoided by splitting frames more equally. In this example, the 675 and 674 bytes large fragment frames could both potentially reach its destination without being too large or too small. Reported-by: Martin Weinelt Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu") Signed-off-by: Sven Eckelmann Acked-by: Linus L?ssing Signed-off-by: Simon Wunderlich [ bp: 4.9 backported: adjust context. ] Signed-off-by: Sven Eckelmann Signed-off-by: Greg Kroah-Hartman --- net/batman-adv/fragmentation.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) --- a/net/batman-adv/fragmentation.c +++ b/net/batman-adv/fragmentation.c @@ -396,7 +396,7 @@ out: * batadv_frag_create - create a fragment from skb * @skb: skb to create fragment from * @frag_head: header to use in new fragment - * @mtu: size of new fragment + * @fragment_size: size of new fragment * * Split the passed skb into two fragments: A new one with size matching the * passed mtu and the old one with the rest. The new skb contains data from the @@ -406,11 +406,11 @@ out: */ static struct sk_buff *batadv_frag_create(struct sk_buff *skb, struct batadv_frag_packet *frag_head, - unsigned int mtu) + unsigned int fragment_size) { struct sk_buff *skb_fragment; unsigned int header_size = sizeof(*frag_head); - unsigned int fragment_size = mtu - header_size; + unsigned int mtu = fragment_size + header_size; skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN); if (!skb_fragment) @@ -449,7 +449,7 @@ int batadv_frag_send_packet(struct sk_bu struct sk_buff *skb_fragment; unsigned int mtu = neigh_node->if_incoming->net_dev->mtu; unsigned int header_size = sizeof(frag_header); - unsigned int max_fragment_size, max_packet_size; + unsigned int max_fragment_size, num_fragments; int ret = -1; /* To avoid merge and refragmentation at next-hops we never send @@ -457,10 +457,15 @@ int batadv_frag_send_packet(struct sk_bu */ mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE); max_fragment_size = mtu - header_size; - max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS; + + if (skb->len == 0 || max_fragment_size == 0) + return -EINVAL; + + num_fragments = (skb->len - 1) / max_fragment_size + 1; + max_fragment_size = (skb->len - 1) / num_fragments + 1; /* Don't even try to fragment, if we need more than 16 fragments */ - if (skb->len > max_packet_size) + if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) goto out; bat_priv = orig_node->bat_priv; @@ -498,7 +503,8 @@ int batadv_frag_send_packet(struct sk_bu goto out; } - skb_fragment = batadv_frag_create(skb, &frag_header, mtu); + skb_fragment = batadv_frag_create(skb, &frag_header, + max_fragment_size); if (!skb_fragment) goto out;