Date: Sun, 4 Apr 2004 13:02:43 +0300 From: Ruslan Ermilov <ru@freebsd.org> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/net if_gif.c Message-ID: <20040404100243.GA16434@ip.net.ua> In-Reply-To: <20040404051126.GA22393@Odin.AC.HMC.Edu> References: <200403221424.i2MEOQYK057524@repoman.freebsd.org> <20040330220349.GA97921@ip.net.ua> <20040330232517.GA19416@Odin.AC.HMC.Edu> <20040331072756.GA14337@ip.net.ua> <20040403085651.GA96868@ip.net.ua> <20040404051126.GA22393@Odin.AC.HMC.Edu>
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--vkogqOf2sHV7VnPd Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Apr 03, 2004 at 09:11:26PM -0800, Brooks Davis wrote: > On Sat, Apr 03, 2004 at 11:56:51AM +0300, Ruslan Ermilov wrote: > > On Wed, Mar 31, 2004 at 10:27:56AM +0300, Ruslan Ermilov wrote: > > > On Tue, Mar 30, 2004 at 03:25:17PM -0800, Brooks Davis wrote: > > > > On Wed, Mar 31, 2004 at 01:03:49AM +0300, Ruslan Ermilov wrote: > > > > > On Mon, Mar 22, 2004 at 06:24:26AM -0800, Robert Watson wrote: > > > > > > rwatson 2004/03/22 06:24:26 PST > > > > > >=20 > > > > > > FreeBSD src repository > > > > > >=20 > > > > > > Modified files: > > > > > > sys/net if_gif.c=20 > > > > > > Log: > > > > > > Move "called", a static function variable used to detect recu= rsive > > > > > > processing with gif interfaces, to a global variable named "g= if_called". > > > > > > Add an annotation that this approach will not work with a ree= ntrant > > > > > > network stack, and that we should instead use packet tags to = detect > > > > > > excessive recursive processing. > > > > > > =20 > > > > > > Revision Changes Path > > > > > > 1.42 +11 -4 src/sys/net/if_gif.c > > > > > >=20 > > > > > Implemented this in the attached patch. Note when testing: setti= ng > > > > > net.link.gif.max_nesting too high (>20 on my system) and triggeri= ng > > > > > the recursion causes the kernel stack exhaustion. > > > >=20 > > > > Why not just do what OpenBSD does and do actual loop detection? Th= is > > > > gets rid of the nesting count hack which isn't really what you want= to > > > > measure anyway. > > > >=20 > > > > http://www.openbsd.org/cgi-bin/cvsweb/src/sys/net/if_gif.c.diff?r1= =3D1.18&r2=3D1.19 > > > >=20 > > > Good idea. I will implement it and repost the updated patch here. > > >=20 > > Actually, just replacing nesting limiter with loop detection was a > > bad idea, so I didn't follow it. It's a bad idea because you might > > have many nesting (but not looping) gif interfaces, and this will > > still cause panic by exhausting the kernel stack. Instead, I have > > combined both checks. Please review the attached patch. >=20 > Unless you can automaticly choose a valid value for max_gif_nesting, I > think it should be taken out and shot. Unless you can do that, there's > nothing you can do to prevent the admin from making a configuration that > blows out the stack so why keep the extra annoyance of gif_max_nest > around? It won't do anything to prevent the panic and will break things > in perfectly valid cases. If we're really worried about the stack > issue, forcing a requeue instead of processing to completion any time > we're nested makes more sense to me. >=20 Unfortunately, there's no such thing as the IP output queue. Anyway, I'm going to commit my version now. If you want to shot the nesting limit, I'm fine with it, but please _you_ do it. ;) Cheers, --=20 Ruslan Ermilov ru@FreeBSD.org FreeBSD committer --vkogqOf2sHV7VnPd Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFAb91DUkv4P6juNwoRAq0WAJ9KZaep3qcYkCFFfAryo04OoQATQgCfVhq/ GtqyHCvsUt3KuLLxkYbrXh4= =ifzQ -----END PGP SIGNATURE----- --vkogqOf2sHV7VnPd--
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