Date: Fri, 16 Dec 2016 23:45:35 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Alan Somers <asomers@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r310180 - head/sys/net Message-ID: <20161216224535.GA6408@dft-labs.eu> In-Reply-To: <201612162239.uBGMdVSL027853@repo.freebsd.org> References: <201612162239.uBGMdVSL027853@repo.freebsd.org>
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On Fri, Dec 16, 2016 at 10:39:31PM +0000, Alan Somers wrote: > Author: asomers > Date: Fri Dec 16 22:39:30 2016 > New Revision: 310180 > URL: https://svnweb.freebsd.org/changeset/base/310180 > > Log: > Fix panic during lagg destruction with simultaneous status check > > If you run "ifconfig lagg0 destroy" and "ifconfig lagg0" at the same time a > page fault may result. The first process will destroy ifp->if_lagg in > lagg_clone_destroy (called by if_clone_destroy). Then the second process > will observe that ifp->if_lagg is NULL at the top of lagg_port_ioctl and > goto fallback: where it will promptly dereference ifp->if_lagg anyway. > > The solution is to repeat the NULL check for ifp->if_lagg > I don't understand how this solves the problem. What prevents the object from getting freed after the pointer got NULLified? That is, it seems the patch turns a null pointer deref into a use-after-free. There seems to be a refcounting issue here. That said, I only did cursory reading. -- Mateusz Guzik <mjguzik gmail.com>
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