Messages in this thread | | | Date | Wed, 21 Sep 2022 20:29:21 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 1/2] fs/exec: switch timens when a task gets a new mm |
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On Tue, Sep 20, 2022 at 05:31:19PM -0700, Andrei Vagin wrote: > From: Andrei Vagin <avagin@gmail.com> > > Changing a time namespace requires remapping a vvar page, so we don't want > to allow doing that if any other tasks can use the same mm. > > Currently, we install a time namespace when a task is created with a new > vm. exec() is another case when a task gets a new mm and so it can switch > a time namespace safely, but it isn't handled now. > > One more issue of the current interface is that clone() with CLONE_VM isn't > allowed if the current task has unshared a time namespace > (timens_for_children doesn't match the current timens). > > Both these issues make some inconvenience for users. For example, Alexey > and Florian reported that posix_spawn() uses vfork+exec and this pattern > doesn't work with time namespaces due to the both described issues. > LXC needed to workaround the exec() issue by calling setns. > > In the commit 133e2d3e81de5 ("fs/exec: allow to unshare a time namespace on > vfork+exec"), we tried to fix these issues with minimal impact on UAPI. But > it adds extra complexity and some undesirable side effects. Eric suggested > fixing the issues properly because here are all the reasons to suppose that > there are no users that depend on the old behavior. > > Cc: Alexey Izbyshev <izbyshev@ispras.ru> > Cc: Christian Brauner <brauner@kernel.org> > Cc: Dmitry Safonov <0x7f454c46@gmail.com> > Cc: "Eric W. Biederman" <ebiederm@xmission.com> > Cc: Florian Weimer <fweimer@redhat.com> > Cc: Kees Cook <keescook@chromium.org> > Suggested-by: "Eric W. Biederman" <ebiederm@xmission.com> > Origin-author: "Eric W. Biederman" <ebiederm@xmission.com> > Signed-off-by: Andrei Vagin <avagin@gmail.com>
This looks good -- my intention is for this to go into -next after the v6.1 merge window closes. Does that match everyone's expectations?
Thanks!
-Kees
-- Kees Cook
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