netdev - Re: Delayed source port allocation for connected UDP sockets

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 for Android: free password hash cracker in your pocket

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

Date:   Wed, 27 Nov 2019 08:18:53 -0800
From:   Maciej Żenczykowski <maze@...gle.com>
To:     Marek Majkowski <marek@...udflare.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        network dev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: Delayed source port allocation for connected UDP sockets

On Wed, Nov 27, 2019 at 8:09 AM Maciej Żenczykowski <maze@...gle.com> wrote:
>
> On Wed, Nov 27, 2019 at 6:08 AM Marek Majkowski <marek@...udflare.com> wrote:
> >
> > Morning,
> >
> > In my applications I need something like a connectx()[1] syscall. On
> > Linux I can get quite far with using bind-before-connect and
> > IP_BIND_ADDRESS_NO_PORT. One corner case is missing though.
> >
> > For various UDP applications I'm establishing connected sockets from
> > specific 2-tuple. This is working fine with bind-before-connect, but
> > in UDP it creates a slight race condition. It's possible the socket
> > will receive packet from arbitrary source after bind():
> >
> > s = socket(SOCK_DGRAM)
> > s.bind((192.0.2.1, 1703))
> > # here be dragons
> > s.connect((198.18.0.1, 58910))
> >
> > For the short amount of time after bind() and before connect(), the
> > socket may receive packets from any peer. For situations when I don't
> > need to specify source port, IP_BIND_ADDRESS_NO_PORT flag solves the
> > issue. This code is fine:
> >
> > s = socket(SOCK_DGRAM)
> > s.setsockopt(IP_BIND_ADDRESS_NO_PORT)
> > s.bind((192.0.2.1, 0))
> > s.connect((198.18.0.1, 58910))
> >
> > But the IP_BIND_ADDRESS_NO_PORT doesn't work when the source port is
> > selected. It seems natural to expand the scope of
> > IP_BIND_ADDRESS_NO_PORT flag. Perhaps this could be made to work:
> >
> > s = socket(SOCK_DGRAM)
> > s.setsockopt(IP_BIND_ADDRESS_NO_PORT)
> > s.bind((192.0.2.1, 1703))
> > s.connect((198.18.0.1, 58910))
> >
> > I would like such code to delay the binding to port 1703 up until the
> > connect(). IP_BIND_ADDRESS_NO_PORT only makes sense for connected
> > sockets anyway. This raises a couple of questions though:
> >
> >  - IP_BIND_ADDRESS_NO_PORT name is confusing - we specify the port
> > number in the bind!
> >
> >  - Where to store the source port in __inet_bind. Neither
> > inet->inet_sport nor inet->inet_num seem like correct places to store
> > the user-passed source port hint. The alternative is to introduce
> > yet-another field onto inet_sock struct, but that is wasteful.
> >
> > Suggestions?
> >
> > Marek
> >
> > [1] https://www.unix.com/man-page/mojave/2/connectx/
>
> attack BPF socket filter drop all, then bind, then connect, then replace it.

Although I guess perhaps you'd consider dropping the packets to be bad...?
Then I think you might be able to do the same trick with
SO_BINDTODEVICE("dummy0") instead of bpf and then SO_BINDTODEVICE("")
That unfortunately requires privs though.