Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754965AbaFQKB6 (ORCPT ); Tue, 17 Jun 2014 06:01:58 -0400 Received: from mail-ie0-f171.google.com ([209.85.223.171]:60511 "EHLO mail-ie0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752272AbaFQKB4 (ORCPT ); Tue, 17 Jun 2014 06:01:56 -0400 MIME-Version: 1.0 In-Reply-To: <53A01049.6020502@redhat.com> References: <1402655819-14325-1-git-send-email-dh.herrmann@gmail.com> <53A01049.6020502@redhat.com> Date: Tue, 17 Jun 2014 12:01:55 +0200 Message-ID: Subject: Re: [PATCH v3 0/7] File Sealing & memfd_create() From: David Herrmann To: Florian Weimer Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , Michael Kerrisk , Ryan Lortie , Linus Torvalds , Andrew Morton , "linux-mm@kvack.org" , Linux FS Devel , Linux API , Greg Kroah-Hartman , John Stultz , Lennart Poettering , Daniel Mack , Kay Sievers , Hugh Dickins , Tony Battersby Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi On Tue, Jun 17, 2014 at 11:54 AM, Florian Weimer wrote: > On 06/13/2014 05:33 PM, David Herrmann wrote: >> >> On Fri, Jun 13, 2014 at 5:17 PM, Andy Lutomirski >> wrote: >>> >>> Isn't the point of SEAL_SHRINK to allow servers to mmap and read >>> safely without worrying about SIGBUS? >> >> >> No, I don't think so. >> The point of SEAL_SHRINK is to prevent a file from shrinking. SIGBUS >> is an effect, not a cause. It's only a coincidence that "OOM during >> reads" and "reading beyond file-boundaries" has the same effect: >> SIGBUS. >> We only protect against reading beyond file-boundaries due to >> shrinking. Therefore, OOM-SIGBUS is unrelated to SEAL_SHRINK. >> >> Anyone dealing with mmap() _has_ to use mlock() to protect against >> OOM-SIGBUS. Making SEAL_SHRINK protect against OOM-SIGBUS would be >> redundant, because you can achieve the same with SEAL_SHRINK+mlock(). > > > I don't think this is what potential users expect because mlock requires > capabilities which are not available to them. > > A couple of weeks ago, sealing was to be applied to anonymous shared memory. > Has this changed? Why should *reading* it trigger OOM? The file might have holes, therefore, you'd have to allocate backing pages. This might hit a soft-limit and fail. To avoid this, use fallocate() to allocate pages prior to mmap() or mlock() to make the kernel lock them in memory. Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/