From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Amit Kapila <amit.kapila16@gmail.com>,
        Dmitry Vasilyev <d.vasilyev@postgrespro.ru>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Tue, 20 Sep 2016 12:32:56 -0400"
Date: Tue, 20 Sep 2016 12:53:54 -0400
Message-ID: <20789.1474390434@sss.pgh.pa.us>
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Robert Haas <robertmhaas@gmail.com> writes:
> Yeah, random() is the wrong thing.  It should use PostmasterRandom().
> Fixed to do that instead.

I am not very happy about this patch; have you considered the security
implications of what you just did?  If you haven't, I'll tell you:
you just made the postmaster's selection of "random" cancel keys and
password salts a lot more predictable.  Formerly, the srandom() seed
for those depended on both the postmaster start time and the time of
the first connection request, but this change removes the first
connection request from the equation.  If you know the postmaster start
time --- which we will happily tell any asker --- it will not take too
many trials to find the seed that's in use.

I'd be the first to agree that this point is inadequately documented
in the code, but PostmasterRandom should be reserved for its existing
security-related uses, not exposed to the world for (ahem) random other
uses.

			regards, tom lane


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