From: Hannes Frederic Sowa Subject: Re: [PATCH, RFC] random: introduce getrandom(2) system call Date: Wed, 23 Jul 2014 14:10:16 +0200 Message-ID: <1406117416.4473.144770005.5B5ED8C2@webmail.messagingengine.com> References: <20140723115253.9808.qmail@ns.horizon.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: George Spelvin , tytso@mit.edu Return-path: In-Reply-To: <20140723115253.9808.qmail@ns.horizon.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Wed, Jul 23, 2014, at 13:52, George Spelvin wrote: > I keep wishing for a more general solution. For example, some way to > have a "spare" extra fd that could be accessed with a special O_NOFAIL > flag. > > That would allow any number of library functions to not fail, such as > logging from nasty corner cases. > > But you'd have to provide one per thread, and block non-fatal signals > while it was open, so you don't get reentrancy problems. Ick. > > > This overly-specialized system call (and worse yet, a blocking > system call that you can't put into a poll() loop) just feels ugly > to me. Is it *absolutely* necessary? One point that often came up besides fd exhaustion is missing /dev/u?random device nodes in chroot environments. I also thought about a more general interface, like e.g. an opennod(dev_t device, int flags) call but all those ideas ended up being very complex changes besides having design issues. getrandom is simple and solves a real problem. The only problem I see, that we allow access to /dev/random without checking any permission bits like we did on opening /dev/random before and we cannot restrict applications to deplete the whole entropy pool. > For example, how about simply making getentropy() a library function that > aborts if it can't open /dev/urandom? If you're suffering fd exhaustion, > you're being DoSed already. Maybe applications want to mitigate fd exhaustion. Bye, Hannes