From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] packet: in packet_snd start writing at link layer allocation Date: Sun, 13 May 2018 20:20:55 -0400 (EDT) Message-ID: <20180513.202055.2059612987939748570.davem@davemloft.net> References: <20180511172425.213901-1-willemdebruijn.kernel@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com, willemb@google.com To: willemdebruijn.kernel@gmail.com Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:51420 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750929AbeENAU5 (ORCPT ); Sun, 13 May 2018 20:20:57 -0400 In-Reply-To: <20180511172425.213901-1-willemdebruijn.kernel@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Willem de Bruijn Date: Fri, 11 May 2018 13:24:25 -0400 > From: Willem de Bruijn > > Packet sockets allow construction of packets shorter than > dev->hard_header_len to accommodate protocols with variable length > link layer headers. These packets are padded to dev->hard_header_len, > because some device drivers interpret that as a minimum packet size. > > packet_snd reserves dev->hard_header_len bytes on allocation. > SOCK_DGRAM sockets call skb_push in dev_hard_header() to ensure that > link layer headers are stored in the reserved range. SOCK_RAW sockets > do the same in tpacket_snd, but not in packet_snd. > > Syzbot was able to send a zero byte packet to a device with massive > 116B link layer header, causing padding to cross over into skb_shinfo. > Fix this by writing from the start of the llheader reserved range also > in the case of packet_snd/SOCK_RAW. > > Update skb_set_network_header to the new offset. This also corrects > it for SOCK_DGRAM, where it incorrectly double counted reserve due to > the skb_push in dev_hard_header. > > Fixes: 9ed988cd5915 ("packet: validate variable length ll headers") > Reported-by: syzbot+71d74a5406d02057d559@syzkaller.appspotmail.com > Signed-off-by: Willem de Bruijn Applied and queued up for -stable, thanks Willem.