From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Alexander E. Patrakov" Subject: Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and introduce getrandom2() Date: Fri, 20 Sep 2019 23:15:01 +0500 Message-ID: <78a4b774-ef6b-62cb-57db-8e1ff8d29f72@gmail.com> References: <20190912034421.GA2085@darwi-home-pc> <20190912082530.GA27365@mit.edu> <20190914122500.GA1425@darwi-home-pc> <008f17bc-102b-e762-a17c-e2766d48f515@gmail.com> <20190915052242.GG19710@mit.edu> <20190918211503.GA1808@darwi-home-pc> <20190918211713.GA2225@darwi-home-pc> <20190920134609.GA2113@pc> Mime-Version: 1.0 Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms010706090605000308010804" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Andy Lutomirski , Linus Torvalds Cc: "Ahmed S. Darwish" , Lennart Poettering , "Theodore Y. Ts'o" , "Eric W. Biederman" , Michael Kerrisk , Willy Tarreau , Matthew Garrett , lkml , Ext4 Developers List , Linux API , linux-man List-Id: linux-api@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms010706090605000308010804 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-PH Content-Transfer-Encoding: quoted-printable 20.09.2019 22:52, Andy Lutomirski =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > I think that, given existing software, we should make two or three > changes to fix the basic problems here: >=20 > 1. Add GRND_INSECURE: at least let new applications do the right thing > going forward. >=20 > 2. Fix what is arguably a straight up kernel bug, not even an ABI > issue: when a user program is blocking in getrandom(..., 0), the > kernel happily sits there doing absolutely nothing and deadlocks the > system as a result. This IMO isn't an ABI issue -- it's an > implementation problem. How about we make getrandom() (probably > actually wait_for_random_bytes()) do something useful to try to seed > the RNG if the system is otherwise not doing IO. >=20 > 3. Optionally, entirely in user code: Get glibc to add new *library* > functions: getentropy_secure_blocking() and getentropy_insecure() or > whatever they want to call them. Deprecate getentropy(). >=20 > I think #2 is critical. Right now, suppose someone has a system that > neets to do a secure network request (a la Red Hat's Clevis). I have > no idea what Clevis actually does, but it wouldn't be particularly > crazy to do a DH exchange or sign with an EC key to ask some network > server to help unlock a dm-crypt volume. If the system does this at > boot, it needs to use getrandom(..., 0), GRND_EXPLICIT, or whatever, > because it NEEDS a secure random number. No about of ABI fiddling > will change this. The kernel should *work* in this case rather than > deadlocking. Let me express a little bit of disagreement with the logic here. I do agree that #2 is critical, and the Clevis use case is a perfect=20 example why it is important. I doubt that it is solvable without=20 trusting jitter entropy, or without provoking a dummy read on a random=20 block device, just for timings, or maybe some other interaction with the = external world - but Willy already said "it seems fishy". However, _if_=20 it is solved, then we don't need GRND_INSECURE, because solving #2 is=20 equivalent to magically making secure random numbers always available. --=20 Alexander E. 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