Date: Sat, 3 Apr 2004 21:11:26 -0800 From: Brooks Davis <brooks@one-eyed-alien.net> To: Ruslan Ermilov <ru@freebsd.org> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/net if_gif.c Message-ID: <20040404051126.GA22393@Odin.AC.HMC.Edu> In-Reply-To: <20040403085651.GA96868@ip.net.ua> 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>
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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 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 recurs= ive > > > > > processing with gif interfaces, to a global variable named "gif= _called". > > > > > Add an annotation that this approach will not work with a reent= rant > > > > > network stack, and that we should instead use packet tags to de= tect > > > > > 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: setting > > > > net.link.gif.max_nesting too high (>20 on my system) and triggering > > > > the recursion causes the kernel stack exhaustion. > > >=20 > > > Why not just do what OpenBSD does and do actual loop detection? This > > > 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=3D= 1.18&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. 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. -- Brooks --=20 Any statement of the form "X is the one, true Y" is FALSE. PGP fingerprint 655D 519C 26A7 82E7 2529 9BF0 5D8E 8BE9 F238 1AD4 --vkogqOf2sHV7VnPd Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (GNU/Linux) iD8DBQFAb5j9XY6L6fI4GtQRAgD9AJ42a72yTFcK25q+ZwRu3UMoPHc+pACdHr1x htNS+o2lGBM9jAC9rUPnoXc= =s4mn -----END PGP SIGNATURE----- --vkogqOf2sHV7VnPd--
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