From: Xie He <xie.he.0141@gmail.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Network Development <netdev@vger.kernel.org>,
syzbot <syzbot+4a2c52677a8a1aa283cb@syzkaller.appspotmail.com>,
William Tu <u9012063@gmail.com>
Subject: Re: [Patch net] ip_gre: set dev->hard_header_len properly
Date: Thu, 8 Oct 2020 12:16:23 -0700 [thread overview]
Message-ID: <CAJht_ENnmYRh-RomBodJE0HoFzaLQhD+DKEu2WWST+B43JxWcQ@mail.gmail.com> (raw)
In-Reply-To: <CA+FuTSdKa1Q36ONbsGOMqXDCUiiDNsA6rkqyrzB+eXJj=MyRKA@mail.gmail.com>
On Thu, Oct 8, 2020 at 12:04 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Thu, Oct 8, 2020 at 1:34 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
> >
> > The uninit data is allocated by packet_alloc_skb(), if dev->hard_header_len
> > is 0 and 'len' is anything between [0, tunnel->hlen + sizeof(struct iphdr)),
> > dev_validate_header() still returns true obviously but only 'len'
> > bytes are copied
> > from user-space by skb_copy_datagram_from_iter(). Therefore, those bytes
> > within range (len, tunnel->hlen + sizeof(struct iphdr)] are uninitialized.
>
> With dev->hard_header_len of zero, packet_alloc_skb() only allocates len bytes.
>
> With SOCK_RAW, the writer is expected to write the ip and gre header
> and include these in the send len argument. The only difference I see
> is that with hard_header_len the data starts reserve bytes before
> skb_network_header, and an additional tail has been allocated that is
> not used.
>
> But this also fixes a potentially more serious bug. With SOCK_DGRAM,
> dev_hard_header/ipgre_header just assumes that there is enough room in
> the packet to skb_push(skb, t->hlen + sizeof(*iph)). Which may be
> false if this header length had not been reserved.
>
> Though I've mainly looked at packet_snd. Perhaps you are referring to
> tpacket_snd?
I think what Cong means is that hard_header_len has to be set properly
to prevent an AF_PACKET/RAW user from sending a frame that is too
short (shorter than the header length). When an AF_PACKET/RAW user
sends a frame shorter than the header length, and the code on the
sending path still expects a full header, it will read uninitialized
data.
If my understanding is right, I agree on this part.
However, there's something I don't understand in the GRE code. The
ipgre_header function only creates an IP header (20 bytes) + a GRE
base header (4 bytes), but pushes and returns "t->hlen +
sizeof(*iph)". What is t->hlen? It seems to me it is the sum of
t->tun_hlen and t->encap_hlen. What are these two?
next prev parent reply other threads:[~2020-10-08 19:16 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 1:21 [Patch net] ip_gre: set dev->hard_header_len properly Cong Wang
2020-10-08 11:48 ` Willem de Bruijn
2020-10-08 17:33 ` Cong Wang
2020-10-08 19:04 ` Willem de Bruijn
2020-10-08 19:16 ` Xie He [this message]
2020-10-08 19:19 ` Willem de Bruijn
2020-10-08 20:10 ` Xie He
2020-10-08 20:31 ` Willem de Bruijn
2020-10-08 21:35 ` Xie He
2020-10-08 21:47 ` Willem de Bruijn
2020-10-08 21:54 ` Xie He
2020-10-08 23:40 ` Xie He
2020-10-09 17:43 ` Cong Wang
2020-10-09 19:41 ` Xie He
2020-10-09 19:51 ` Xie He
2020-10-09 20:38 ` Cong Wang
2020-10-10 1:07 ` Cong Wang
2020-10-10 3:10 ` Xie He
2020-10-10 18:58 ` Cong Wang
2020-10-10 21:49 ` Xie He
2020-10-11 3:55 ` Xie He
2020-10-11 14:35 ` Xie He
2020-10-08 19:18 ` Willem de Bruijn
2020-10-08 19:50 ` Cong Wang
2020-10-08 20:19 ` Willem de Bruijn
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