From: Andrei Vagin <avagin@gmail.com>
To: Giuseppe Scrivano <gscrivan@redhat.com>
Cc: Colin Walters <walters@verbum.org>,
Christian Brauner <brauner@kernel.org>,
Aleksa Sarai <cyphar@cyphar.com>,
linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
bristot@redhat.com, "Eric W. Biederman" <ebiederm@xmission.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Alexander Larsson <alexl@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
bmasney@redhat.com
Subject: Re: [PATCH v3 1/2] exec: add PR_HIDE_SELF_EXE prctl
Date: Fri, 24 Feb 2023 16:27:19 -0800 [thread overview]
Message-ID: <Y/lV53Dc+zwj2dla@gmail.com> (raw)
In-Reply-To: <20230130100602.elyvs6oorfzukjwh@wittgenstein>
On Mon, Jan 30, 2023 at 11:06:02AM +0100, Christian Brauner wrote:
> On Mon, Jan 30, 2023 at 10:53:31AM +0100, Christian Brauner wrote:
> > On Sun, Jan 29, 2023 at 01:12:45PM -0500, Colin Walters wrote:
> > >
> > >
> > > On Sun, Jan 29, 2023, at 11:58 AM, Christian Brauner wrote:
> > > > On Sun, Jan 29, 2023 at 08:59:32AM -0500, Colin Walters wrote:
> > > >>
> > > >>
> > > >> On Wed, Jan 25, 2023, at 11:30 AM, Giuseppe Scrivano wrote:
> > > >> >
> > > >> > After reading some comments on the LWN.net article, I wonder if
> > > >> > PR_HIDE_SELF_EXE should apply to CAP_SYS_ADMIN in the initial user
> > > >> > namespace or if in this case root should keep the privilege to inspect
> > > >> > the binary of a process. If a container runs with that many privileges
> > > >> > then it has already other ways to damage the host anyway.
> > > >>
> > > >> Right, that's what I was trying to express with the "make it work the same as map_files". Hiding the entry entirely even for initial-namespace-root (real root) seems like it's going to potentially confuse profiling/tracing/debugging tools for no good reason.
> > > >
> > > > If this can be circumvented via CAP_SYS_ADMIN
> > >
> > > To be clear, I'm proposing CAP_SYS_ADMIN in the current user namespace at the time of the prctl(). (Or if keeping around a reference just for this is too problematic, perhaps hardcoding to the init ns)
> >
> > Oh no, I fully understand. The point was that the userspace fix protects
> > even against attackers with CAP_SYS_ADMIN in init_user_ns. And that was
> > important back then and is still relevant today for some workloads.
> >
> > For unprivileged containers where host and container are separate by a
> > meaningful user namespace boundary this whole mitigation is irrelevant
> > as the binary can't be overwritten.
> >
> > >
> > > A process with CAP_SYS_ADMIN in a child namespace would still not be able to read the binary.
> > >
> > > > then this mitigation
> > > > becomes immediately way less interesting because the userspace
> > > > mitigation we came up with protects against CAP_SYS_ADMIN as well
> > > > without any regression risk.
> > >
> > > The userspace mitigation here being "clone self to memfd"? But that's a sufficiently ugly workaround that it's created new problems; see https://lwn.net/Articles/918106/
> >
> > But this is a problem with the memfd api not with the fix. Following the
> > thread the ability to create executable memfds will stay around. As it
> > should be given how long this has been supported. And they have backward
> > compatibility in mind which is great.
>
> Following up from yesterday's promise to check with the criu org I'm
> part of: this is going to break criu unforunately as it dumps (and
> restores) /proc/self/exe. Even with an escape hatch we'd still risk
> breaking it. Whereas again, the memfd solution doesn't cause those
> issues.
>
> Don't get me wrong it's pretty obvious that I was pretty supportive of
> this fix especially because it looked rather simple but this is turning
> out to be less simple than we tought. I don't think that this is worth
> it given the functioning fixes we already have.
btw: can we use PR_SET_MM_EXE_FILE or PR_SET_MM_MAP (prctl_map.exe_fd) to
set a dummy exe. Will it have the required effect?
>
> The good thing is that - even if it will take a longer - that Aleksa's
> patchset will provide a more general solution by making it possible for
> runc/crun/lxc to open the target binary with a restricted upgrade mask
> making it impossible to open the binary read-write again. This won't
> break criu and will fix this issue and is generally useful.
next prev parent reply other threads:[~2023-02-25 0:27 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-20 10:25 [PATCH v3 1/2] exec: add PR_HIDE_SELF_EXE prctl Giuseppe Scrivano
2023-01-20 10:25 ` [PATCH v3 2/2] selftests: add tests for prctl(SET_HIDE_SELF_EXE) Giuseppe Scrivano
2023-01-20 16:05 ` Brian Masney
2023-01-23 18:41 ` [PATCH v3 1/2] exec: add PR_HIDE_SELF_EXE prctl Colin Walters
2023-01-23 19:21 ` Giuseppe Scrivano
2023-01-23 22:07 ` Colin Walters
2023-01-23 22:54 ` Giuseppe Scrivano
2023-01-23 23:14 ` Colin Walters
2023-01-24 1:53 ` Aleksa Sarai
2023-01-24 7:29 ` Giuseppe Scrivano
2023-01-25 15:28 ` Aleksa Sarai
2023-01-25 16:30 ` Giuseppe Scrivano
2023-01-29 13:59 ` Colin Walters
2023-01-29 16:58 ` Christian Brauner
2023-01-29 18:12 ` Colin Walters
2023-01-30 9:53 ` Christian Brauner
2023-01-30 10:06 ` Christian Brauner
2023-01-30 21:52 ` Colin Walters
2023-01-31 14:17 ` Giuseppe Scrivano
2023-02-25 0:27 ` Andrei Vagin [this message]
2023-02-28 14:19 ` Giuseppe Scrivano
2023-01-26 8:25 ` Christian Brauner
2023-01-24 19:17 ` Andrei Vagin
2023-01-27 12:31 ` Christian Brauner
2023-01-27 20:34 ` Kees Cook
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