netdev - [RFC] tcp: randomize TCP source ports

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-next>] [day] [month] [year] [list]

Message-ID: <1383872049.9412.124.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 07 Nov 2013 16:54:09 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [RFC] tcp: randomize TCP source ports

TCP does proper randomization of ports on active connections only if
bind() is used between socket() and connect()

If bind() is not specifically used, kernel performs autobind, and TCP
autobind typically uses a sequential allocation for a given (dst
address, dst port, src address) tuple.

UDP autobind does a randomization, as part of the effort to make DNS
more secure.

TCP autobind uses a global sequential number (called @hint in source
code) with a perturbation done by secure_ipv4_port_ephemeral(),
 so that the 'hint' of the next port is per (saddr, daddr, dport) tuple

This was probably done to maximize port use and avoid hitting timewait
sockets, but I think it should be OK to replace this stuff by a random
selection to have more entropy in the various flow hashing functions,
and in general higher security levels. TCP timestamps are now well
deployed.

Patch would be trivial, but I'd like to get some comments if
you think this idea is wrong.

Thanks !

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html