Date: Tue, 16 Sep 2014 12:42:36 +0200 From: Mateusz Guzik <mjguzik@gmail.com> To: Peter Wemm <peter@wemm.org> Cc: Patrick Kelsey <kelsey@ieee.org>, George Neville-Neil <gnn@freebsd.org>, freebsd-current@freebsd.org Subject: Re: _ftello() modification requires additional capsicum rights, breaking tcpdump and dhclient Message-ID: <20140916104236.GA21560@dft-labs.eu> In-Reply-To: <4252906.DAHIEnKpIF@overcee.wemm.org> References: <CAD44qMWgWn_OZ1i0Jy2WTLY=YAai%2B6-_Bq24QN-AjD9iYJ2JOA@mail.gmail.com> <540FF706.2050400@freebsd.org> <CAD44qMV_AVYO2nwUJO27T8MYbacj2GgxectXtBuHU2qnWq_Ppw@mail.gmail.com> <4252906.DAHIEnKpIF@overcee.wemm.org>
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On Fri, Sep 12, 2014 at 09:29:56PM -0700, Peter Wemm wrote: > On Thursday, September 11, 2014 12:38:02 PM Patrick Kelsey wrote: > > On Wed, Sep 10, 2014 at 3:00 AM, Andrey Chernov <ache@freebsd.org> wrote: > > > On 09.09.2014 21:53, Patrick Kelsey wrote: > > > > I don't think it is worth the trouble, as given the larger pattern of > > > > libc routines requiring multiple capsicum rights, it seems one will in > > > > general have to have libc implementation knowledge when using it in > > > > concert with capsicum. For example, consider the limitfd() routine in > > > > kdump.c, which provides rights for the TIOCGETA ioctl to be used on > > > > stdout so the eventual call to isatty() via printf() will work as > > > > > > intended. > > > > > > > I think the above kdump example is a good one for the subtle issues that > > > > can arise when using capsicum with libc. That call to isatty() is via a > > > > widely-used internal libc routine __smakebuf(). __smakebuf() also calls > > > > __swhatbuf(), which in turn calls _fstat(), all to make sure that output > > > > to a tty is line buffered by default. It would appear that programs > > > > that restrict rights on stdout without allowing CAP_IOCTL and CAP_FSTAT > > > > could be disabling the normally default line buffering when stdout is a > > > > tty. kdump goes the distance, but dhclient does not (restricting stdout > > > > to CAP_WRITE only). > > > > > > > > In any event, the patch attached to my first message is seeming like the > > > > way to go. > > > > > > Well, then commit it (if capsicum team agrees). > > > > Will do - thanks for the feedback. > > > > -Patrick > > Is there any possibility that this is related to the problem we've recently > hit in the freebsd.org cluster with this month's refresh? > > After running for a while: > Sep 10 02:39:44 ns2 unbound: [65258:0] notice: init module 0: validator > Sep 10 02:39:44 ns2 unbound: [65258:0] notice: init module 1: iterator > Sep 10 11:44:29 ns2 unbound: [65258:3] fatal error: event_dispatch returned > error -1, errno is Capabilities insufficient > > Sep 10 16:21:16 ns2 unbound: [28212:0] warning: did not exit gracefully last > time (65258) > Sep 10 16:21:16 ns2 unbound: [28213:0] notice: init module 0: validator > Sep 10 16:21:16 ns2 unbound: [28213:0] notice: init module 1: iterator > Sep 11 10:23:49 ns2 unbound: [28213:5] fatal error: event_dispatch returned > error -1, errno is Capabilities insufficient > > Sep 11 13:48:46 ns2 unbound: [79419:0] warning: did not exit gracefully last > time (28213) > Sep 11 13:48:46 ns2 unbound: [79420:0] notice: init module 0: validator > Sep 11 13:48:46 ns2 unbound: [79420:0] notice: init module 1: iterator > Sep 11 18:42:56 ns2 unbound: [79420:6] fatal error: event_dispatch returned > error -1, errno is Capabilities insufficient > > I believe this jail was started from the boot process. If I restart the jail > by hand from a ssh session the problem goes away. > > This is unbound from ports and I don't have any more details than this. This > is new this month. > Is this thingy multithreaded? Currently there is a race in the kernel where fd is visible before relevant capabilities are installed. This can result in an error like this one for weird processes. I got a patch for this: http://lists.freebsd.org/pipermail/freebsd-arch/2014-August/015788.html but it got stalled on 'memory barrier' discussion. I'll try to ping people to move it forward. IIRC there was a report of unbound failing this way, apparently fixed with aforementioned patch. -- Mateusz Guzik <mjguzik gmail.com>
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