From owner-freebsd-current@FreeBSD.ORG Mon Sep 29 18:53:09 2014 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 5C6D9267 for ; Mon, 29 Sep 2014 18:53:09 +0000 (UTC) Received: from spindle.one-eyed-alien.net (spindle.one-eyed-alien.net [199.48.129.229]) by mx1.freebsd.org (Postfix) with ESMTP id 352B6666 for ; Mon, 29 Sep 2014 18:53:08 +0000 (UTC) Received: by spindle.one-eyed-alien.net (Postfix, from userid 3001) id 135F05A9F24; Mon, 29 Sep 2014 18:53:08 +0000 (UTC) Date: Mon, 29 Sep 2014 18:53:08 +0000 From: Brooks Davis To: Luigi Rizzo Subject: Re: capsicum and netmap ? Message-ID: <20140929185308.GD99239@spindle.one-eyed-alien.net> References: <20140929153043.GA78397@onelab2.iet.unipi.it> <20140929172709.GC99239@spindle.one-eyed-alien.net> <20140929182008.GD78397@onelab2.iet.unipi.it> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="zS7rBR6csb6tI2e1" Content-Disposition: inline In-Reply-To: <20140929182008.GD78397@onelab2.iet.unipi.it> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: current@freebsd.org X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 29 Sep 2014 18:53:09 -0000 --zS7rBR6csb6tI2e1 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 29, 2014 at 08:20:08PM +0200, Luigi Rizzo wrote: > On Mon, Sep 29, 2014 at 05:27:09PM +0000, Brooks Davis wrote: > > On Mon, Sep 29, 2014 at 05:30:43PM +0200, Luigi Rizzo wrote: > > >=20 > > > Hi, > > > while trying the netmap-enabled libpcap library with tcpdump, i > > > noticed it fails to return data on a kernel with capsicum (the > > > string "capability mode sandbox enabled" made me suspicious, and > > > removing the cap_*() calls from tcpdump.c seems to make things > > > work again). > > >=20 > > > Would anyone be able to point me what should be done in the netmap > > > kernel module to make it work with capsicum ? > > >=20 > > > I am sure the cambridge folks are very interested in this :) > >=20 > > Without knowing what modifications have been made to libpcap, it's hard > > to say what you need to change, but the short version is that once > > cap_enter is called, you must not attempt to open any file handles as > > that's won't work. I can't think of any other likely cause. Are all > > the returns of all open(), socket(), etc calls checked? >=20 > Hi Brooks, > thanks for the feedback. >=20 > The change (attached, with some debugging code; it dates back to > december and i am trying to upstream it into FreeBSD now) is a set > of methods called to open, dispatch and inject packets. >=20 > > In practice that means that either opening files must come earlier, or > > a singling mechanism needs to be added to tcpdump and libpcap to tell > > tcpdump not to enter capability mode when using netmap. >=20 > The nm_open() (which includes open and mmap) occurs before the > cap_enter() call, and poll() works fine until we do the > cap_enter()/cap_sandboxed() calls. >=20 > I was wondering whether I should somewhat annotate the file descriptor > (in the netmap kernel module) indicating that it is right to access it > after cap_enter(). poll() returns 1 and errno=3D0 > when polling for POLLIN on the netmap file descriptor, > while it should return 0 (there is no traffic queued). >=20 > I haven't investigated in detail but it almost looks like the > underlying netmap_poll() in the device driver is not called. Ah, that's it. The problem is that we're limiting the pcap file descriptors to CAP_READ. It looks like you'd need to add CAP_EVENT to that list. Look for cap_rights_init and cap_rights_limit pairs to find the right place(s) to modify. -- Brooks --zS7rBR6csb6tI2e1 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlQpqpMACgkQXY6L6fI4GtRYQQCfTLk0ftRawbsSx+yK4gXxHHAu R7QAn2WKpNoN6PEPCKDpYM/HDXSLXJkx =z6NE -----END PGP SIGNATURE----- --zS7rBR6csb6tI2e1--