netdev - Re: [PATCH net] packet: in packet_snd start writing at link layer allocation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 24 May 2018 13:01:45 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Tariq Toukan <tariqt@...lanox.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Maor Gottlieb <maorg@...lanox.com>
Subject: Re: [PATCH net] packet: in packet_snd start writing at link layer allocation

On Thu, May 24, 2018 at 11:17 AM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> On Thu, May 24, 2018 at 11:07 AM, Tariq Toukan <tariqt@...lanox.com> wrote:
>>
>>
>> On 14/05/2018 3:20 AM, David Miller wrote:
>>>
>>> From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
>>> Date: Fri, 11 May 2018 13:24:25 -0400
>>>
>>>> From: Willem de Bruijn <willemb@...gle.com>
>>>>
>>>> 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@...kaller.appspotmail.com
>>>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>>>
>>>
>>> Applied and queued up for -stable, thanks Willem.
>>>
>>
>> Hi,
>>
>> One of our regression tests started failing. Once this patch is reverted,
>> test passes.
>>
>> The tests add flow steering rules in the receiver side and in the sender
>> side it send the packet with some RAW socket applications. Then received
>> side gets completion with error.
>>
>> Our verification team compared the packets between the stable and the broken
>> version, in the broken version we have some extra bytes at the end of the
>> packet.
>>
>> It looks like some bad push to the SKB, maybe the conditional reserved
>> addition should be more strict?
>>
>> Any idea?
>
> Thanks for reporting, sorry for the breakage.
>
> I think I might. This skb_push moves back the start of skb->data in the
> same way that tpacket_snd does. But it does not reduce the length
> passed to skb_put, so this might double count hard_header_len.
>
> Let me construct a test.

Indeed.

Still verifying, but this almost certainly has to be

  @@ -2911,7 +2912,7 @@ static int packet_snd(struct socket *sock,
struct msghdr *msg, size_t len)
                  if (unlikely(offset < 0))
                          goto out_free;
          } else if (reserve) {
  -               skb_push(skb, reserve);
  +               skb_reserve(skb, -reserve);
          }

to move the start of the packet without changing its length.