Date: Sat, 20 Sep 2008 16:27:03 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Maksim Yevmenkin <maksim.yevmenkin@gmail.com> Cc: Alexey Shuvaev <shuvaev@physik.uni-wuerzburg.de>, freebsd-current@freebsd.org Subject: Re: Interface auto-cloning bug or feature? Message-ID: <20080920132703.GG47828@deviant.kiev.zoral.com.ua> In-Reply-To: <bb4a86c70809191543y7f3d38ex73c48186dfd163c5@mail.gmail.com> References: <48D2F942.4070801@FreeBSD.org> <20080919084201.GD44330@wep4035.physik.uni-wuerzburg.de> <48D38DFF.8000803@FreeBSD.org> <20080919203310.GA34131@localhost.my.domain> <bb4a86c70809191543y7f3d38ex73c48186dfd163c5@mail.gmail.com>
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[-- Attachment #1 --] On Fri, Sep 19, 2008 at 03:43:21PM -0700, Maksim Yevmenkin wrote: > [....] > > >> That what has caused me to look into this issue. You can find patch for > >> security/vpnc to prevent unbounded interface cloning here: > >> > >> http://sobomax.sippysoft.com/~sobomax/vpnc.diff > >> > > Ok, the patch prevents interface cloning, but I think it doesn't solve > > the actual problem. > > Let's wait for Maksim :) > > ok, how about attached patch. i put it together *very* quickly and > only gave it a light testing. its for tap(4), because i could compile > it as a module and tun(4) is compiled into kernel by default, but the > idea should identical for tun(4). should be even simpler for tun(4) > because it does not have to deal with 2 kind of devices (i.e. tap and > vmnet). give it a try, and see if it works. please try both cloning > paths, i.e. > > 1) cat /dev/tap (/dev/vmnet) with and/or without unit number > > and > > 2) ifconfig tapX (vmnetX) create/destroy > > in the mean time i will prepare something similar for tun(4). > > thanks, > max > --- if_tap.c.orig 2008-09-08 17:20:57.000000000 -0700 > +++ if_tap.c 2008-09-19 15:35:02.000000000 -0700 > @@ -94,6 +94,7 @@ > static int tapifioctl(struct ifnet *, u_long, caddr_t); > static void tapifinit(void *); > > +static int tap_clone_lookup(struct cdev **, u_short); > static int tap_clone_create(struct if_clone *, int, caddr_t); > static void tap_clone_destroy(struct ifnet *); > static int vmnet_clone_create(struct if_clone *, int, caddr_t); > @@ -176,6 +177,28 @@ > DEV_MODULE(if_tap, tapmodevent, NULL); > > static int > +tap_clone_lookup(struct cdev **dev, u_short extra) > +{ > + struct tap_softc *tp; > + > + mtx_lock(&tapmtx); > + SLIST_FOREACH(tp, &taphead, tap_next) { > + mtx_lock(&tp->tap_mtx); > + if ((tp->tap_flags & (TAP_OPEN|extra)) == extra) { > + *dev = tp->tap_dev; > + mtx_unlock(&tp->tap_mtx); > + mtx_unlock(&tapmtx); > + > + return (1); > + } > + mtx_unlock(&tp->tap_mtx); > + } > + mtx_unlock(&tapmtx); > + > + return (0); > +} > + > +static int > tap_clone_create(struct if_clone *ifc, int unit, caddr_t params) > { > struct cdev *dev; > @@ -353,8 +376,18 @@ > > /* We're interested in only tap/vmnet devices. */ > if (strcmp(name, TAP) == 0) { > + if (tap_clone_lookup(dev, 0)) { > + dev_ref(*dev); > + return; What would prevent two concurrent threads from selecting the same device there ? First thread could look up the device, unloc tapmtx and be preempted. Then second thread is put on CPU, do the same selection. Now you have a problem. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkjU+iYACgkQC3+MBN1Mb4g78wCfddJKStzNj9xTz79XbtUJ8do0 zqkAoJY/J9EELGG2kCa1Lz++C7/U7Gwg =t1a/ -----END PGP SIGNATURE-----help
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