Date: Mon, 29 Sep 2014 20:20:08 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Brooks Davis <brooks@freebsd.org> Cc: current@freebsd.org Subject: Re: capsicum and netmap ? Message-ID: <20140929182008.GD78397@onelab2.iet.unipi.it> In-Reply-To: <20140929172709.GC99239@spindle.one-eyed-alien.net> References: <20140929153043.GA78397@onelab2.iet.unipi.it> <20140929172709.GC99239@spindle.one-eyed-alien.net>
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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: > > > > 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). > > > > Would anyone be able to point me what should be done in the netmap > > kernel module to make it work with capsicum ? > > > > I am sure the cambridge folks are very interested in this :) > > 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? Hi Brooks, thanks for the feedback. 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. > 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. 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. 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=0 when polling for POLLIN on the netmap file descriptor, while it should return 0 (there is no traffic queued). I haven't investigated in detail but it almost looks like the underlying netmap_poll() in the device driver is not called. cheers luigi
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