On Fri, Dec 16, 2016 at 3:45 PM, Mateusz Guzik <mjgu...@gmail.com> wrote: > 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.
What object are you talking about? The problem solved by this commit is the null-pointer dereference in the thread calling lagg_port_ioctl, for example "ifconfig lagg0". _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
