Re: Concurrent access to /dev/urandom

Theodore Ts'o
2004-12-11T17:33:45Z

On Fri, Dec 10, 2004 at 06:22:37PM -0600, Adam Heath wrote:
>
> Actually, I think this is a security issue. Since any plain old program can
> read from /dev/urandom at any time, an attacker could attempt to read from
> that device at the same moment some other program is doing so, and thereby
> gain some knowledge as to the other program's state.

It could be a potential exploit, but....

(a) it only applies on SMP machines
(b) it's not a remote exploit; the attacker needs to have
the ability to run arbitrary programs on the local
machine
(c) the attacker won't get all of other programs' reads of
/dev/urandom, and
(d) the attacker would have to have a program continuously
reading from /dev/urandom, which would take up enough
CPU time that it would be rather hard to hide.

That's not to say that we shouldn't fix it at our earliest
convenience, and I'd urge Andrew to push this to Linus for 2.6.10 ---
but I don't think we need to move heaven and earth to try to
accelerate the 2.6.10 release process, either.

- Ted