Messages in this thread | | | Date | Sat, 15 Mar 2008 13:34:26 +0000 | From | Alan Cox <> | Subject | Re: SO_REUSEADDR not allowing server and client to use same port |
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On Thu, 13 Mar 2008 14:18:15 -0500 Nebojsa Miljanovic <neb@alcatel-lucent.com> wrote:
> Alan, > I would appreciate it if you could elaborate on the security issue. Can you > describe the simultaneous connect scenario? > > We have a system we are migrating to Linux from Lynx. We have always had the > ability to re-use ports. We are wondering if this security issue is something we > should take seriously. Or, maybe it is not likely to be seen with our system > running well defined set of applications (i.e. not a PC where anybody could run > anything).
See RFC 793. It is permissible for a connection to be created between two end points both making a connection (crossing SYN frames are both acked). Thus if you allow such reuse it is possible (although usually very very hard) to mount a timing based attack.
It's not a very practical attack in most scenarios so we block it out of correctness and concerns for completely robust and proper behaviour rather than because it is seen in the wild.
Alan
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