[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] libs/light: make it build without setresuid()
On Wed, Jan 20, 2021 at 02:52:06PM +0000, Ian Jackson wrote: > Roger Pau Monné writes ("Re: [PATCH] libs/light: make it build without > setresuid()"): > > On Tue, Jan 12, 2021 at 07:12:36PM +0100, Manuel Bouyer wrote: > > > From: Manuel Bouyer <bouyer@xxxxxxxxxx> > > > > > > NetBSD doesn't have setresuid(). Add a configure check for it, > > > and use plain setuid() if !HAVE_SETRESUID > ... > > LGTM from a code PoV, but I think George/Ian should take a look, since > > they know exactly what this is supposed to do, and I would bet there > > are some reasons why setresuid is used instead of setuid, which should > > likely be taken into account in the commit message to justify why > > using setuid in it's place it's fine. > > There is indeed a reason for using setresuid here. See the comments > at the top of kill_device_model_uid_child and the commit messages for > 87f9458e3400 and 0c653574d39c. This is all quite complex: > > https://xenproject.org/2018/08/01/killing-processes-that-dont-want-to-be-killed/ > > https://marc.info/?l=xen-devel&m=152215770803468 > (search in that message for "libxl UID cleanup") > > I wrote a message to George in 2018 proving that the desired set of > IDs cannot be made without setresuid. I'll c&p the relevant part below. > > I don't think setuid is safe - at least, if we are trying to restrict > the dm. Since I think after the libxl child is forked, and has called What is the dm in this case ? qemu ? On NetBSD qemu runs as root AFAIK, so there isn't much to protect. > setuid, it might be traceable (by NetBSD's equivalent of ptrace) by > the dm. The dm could puppet it into pretending it had succeeded, but > then hang around until the domid is reused. I don't understand. We're talking about a simple kill(2) syscall here. > > At the very least, this patch needs an argument, in detail, why this > is OK. > > Also, why oh why does NetBSD not have setresuid ?? It's at least 20 > years old ! It's not because it's old that it's good. > > Sorry, OK so if I understand properly, you say Xen should not be used on NetBSD ? -- Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx> NetBSD: 26 ans d'experience feront toujours la difference --
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