Date: Fri, 20 Dec 2002 02:12:16 -0600 From: Sean Kelly <smkelly@zombie.org> To: Nate Lawson <nate@root.org> Cc: current@freebsd.org Subject: Re: `cat /dev/io` leads to system lockup. Message-ID: <20021220081215.GA35355@edgemaster.zombie.org> In-Reply-To: <Pine.BSF.4.21.0212192333210.61220-100000@root.org> References: <20021220062935.GA699@edgemaster.zombie.org> <Pine.BSF.4.21.0212192333210.61220-100000@root.org>
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--sdtB3X0nJg68CQEu Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Dec 19, 2002 at 11:35:01PM -0800, Nate Lawson wrote: > On Fri, 20 Dec 2002, Sean Kelly wrote: > > On my 5.0-CURRENT kernel built 45 minutes ago, I can bring my system to= its > > knees by doing > >=20 > > # cat /dev/io > >=20 > > While I understand that this isn't exactly something one would normally= be > > doing, is it really something that should bring the system down? >=20 > You're running as root. So does "yes > /dev/da0" and "cat /dev/urandom > > /dev/mem" and ... (infinity) While I don't really care to test it, I wager that `yes >/dev/da0` will not cause the system to lock hard. But you seem to be talking abot something very different. You are talking about WRITING. I am talking about READING. # cat /dev/da0 # cat /dev/urandom None of these bring the system to its knees. So why does # cat /dev/io totally lock my system solid? According to the manpage: The special file /dev/io is a controlled security hole that allows a pro- cess to gain I/O privileges (which are normally reserved for kernel- internal code). Any process that holds a file descriptor on /dev/io open will get its IOPL bits in the flag register set, thus allowing it to per- form direct I/O operations. =20 This says nothing about what happens if you attempt to read() from /dev/io, as `cat /dev/io` would be expected to do. At the least, there should be a big, fat, blinking WARNING on the manpage telling you that `cat /dev/io` wi= ll bring your system down. --=20 Sean Kelly | PGP KeyID: D2E5E296 smkelly@zombie.org | http://www.zombie.org --sdtB3X0nJg68CQEu Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (FreeBSD) iD8DBQE+AtDfPm7A9NLl4pYRAoDzAJ4y3u/8ueWaibL9S3n6nxAkeozO9QCgzmHy ygdiWHnsYrwhXuAp2hopams= =wY4c -----END PGP SIGNATURE----- --sdtB3X0nJg68CQEu-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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