linux-kernel - Re: [kernel-hardening] Re: [PATCH v4 13/13] random: warn when kernel uses unseeded randomness

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

Message-ID: <20170618154625.5qu3eduqjtgk5bal@thunk.org>
Date:   Sun, 18 Jun 2017 11:46:25 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Stephan Müller <smueller@...onox.de>
Cc:     kernel-hardening@...ts.openwall.com,
        Michael Ellerman <mpe@...erman.id.au>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Miller <davem@...emloft.net>,
        Eric Biggers <ebiggers3@...il.com>
Subject: Re: [kernel-hardening] Re: [PATCH v4 13/13] random: warn when kernel
 uses unseeded randomness

On Thu, Jun 15, 2017 at 01:59:43PM +0200, Stephan Müller wrote:
> I would think that the issue regarding the logging is relevant for 
> cryptographic use cases or use cases requiring strong random numbers only. 
> Only those use cases should be fixed eventually to wait for a fully seeded 
> DRNG.
> 
> The logged messages you present here indicate use cases where no strong 
> security is required. It looks like that the logs show ASLR related use of 
> random numbers. Those do not require a fully seeded ChaCha20 DRNG.

I suspect there is a range of opinions aobut whether or not ASLR
requires strongly secure random numbers or not.  It seems pretty clear
that if we proposed using prandom_u32 for ASLR, people would object
very strongly indeed, since that would make it trivially easy for
attackers to circumvent ASLR protections.

> IMHO, users using the get_random_u64 or get_random_u32 are use cases that do 
> not require a fully seeded DRNG thus do not need a cryptographically strong 
> random number. Hence, I would think that the logging should be removed from 
> get_random_u32/u64.

You are effectively proposing that there ought to be a middle range of
security between prandom_32, get_random_u32/get_random_u64 and
get_random_bytes().  I think that's going to lead to all sorts of
complexity and bugs from people not understanding when they should use
get_random_u32 vs get_random_bytes versus prandom_u32.  And then we'll
end up needing to audit all of the callsites for get_random_u32() so
they don't violate this new usage rule that you are proposing.

     	   	   	    	       - Ted