linux-toradex.git/kernel/time/namespace.c, branch v5.9-rc6

nsproxy: support CLONE_NEWTIME with setns()

2020-07-08T09:14:22+00:00

So far setns() was missing time namespace support. This was partially due
to it simply not being implemented but also because vdso_join_timens()
could still fail which made switching to multiple namespaces atomically
problematic. This is now fixed so support CLONE_NEWTIME with setns()

Signed-off-by: Christian Brauner 
Reviewed-by: Andrei Vagin 
Cc: Thomas Gleixner 
Cc: Michael Kerrisk 
Cc: Serge Hallyn 
Cc: Dmitry Safonov 
Link: https://lore.kernel.org/r/20200706154912.3248030-4-christian.brauner@ubuntu.com

timens: add timens_commit() helper

2020-07-08T09:14:21+00:00

Wrap the calls to timens_set_vvar_page() and vdso_join_timens() in
timens_on_fork() and timens_install() in a new timens_commit() helper.
We'll use this helper in a follow-up patch in nsproxy too.

Signed-off-by: Christian Brauner 
Reviewed-by: Andrei Vagin 
Cc: Will Deacon 
Cc: Vincenzo Frascino 
Cc: Thomas Gleixner 
Cc: Catalin Marinas 
Cc: Mark Rutland 
Cc: Dmitry Safonov 
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20200706154912.3248030-3-christian.brauner@ubuntu.com

timens: make vdso_join_timens() always succeed

2020-07-08T09:14:21+00:00

As discussed on-list (cf. [1]), in order to make setns() support time
namespaces when attaching to multiple namespaces at once properly we
need to tweak vdso_join_timens() to always succeed. So switch
vdso_join_timens() to using a read lock and replacing
mmap_write_lock_killable() to mmap_read_lock() as we discussed.

Last cycle setns() was changed to support attaching to multiple namespaces
atomically. This requires all namespaces to have a point of no return where
they can't fail anymore. Specifically, _install() is
allowed to perform permission checks and install the namespace into the new
struct nsset that it has been given but it is not allowed to make visible
changes to the affected task. Once _install() returns
anything that the given namespace type requires to be setup in addition
needs to ideally be done in a function that can't fail or if it fails the
failure is not fatal. For time namespaces the relevant functions that fall
into this category are timens_set_vvar_page() and vdso_join_timens().
Currently the latter can fail but doesn't need to. With this we can go on
to implement a timens_commit() helper in a follow up patch to be used by
setns().

[1]: https://lore.kernel.org/lkml/20200611110221.pgd3r5qkjrjmfqa2@wittgenstein

Signed-off-by: Christian Brauner 
Reviewed-by: Andrei Vagin 
Cc: Will Deacon 
Cc: Vincenzo Frascino 
Cc: Thomas Gleixner 
Cc: Andy Lutomirski 
Cc: Catalin Marinas 
Cc: Mark Rutland 
Cc: Dmitry Safonov 
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20200706154912.3248030-2-christian.brauner@ubuntu.com

nsproxy: add struct nsset

2020-05-09T11:57:12+00:00

Add a simple struct nsset. It holds all necessary pieces to switch to a new
set of namespaces without leaving a task in a half-switched state which we
will make use of in the next patch. This patch switches the existing setns
logic over without causing a change in setns() behavior. This brings
setns() closer to how unshare() works(). The prepare_ns() function is
responsible to prepare all necessary information. This has two reasons.
First it minimizes dependencies between individual namespaces, i.e. all
install handler can expect that all fields are properly initialized
independent in what order they are called in. Second, this makes the code
easier to maintain and easier to follow if it needs to be changed.

The prepare_ns() helper will only be switched over to use a flags argument
in the next patch. Here it will still use nstype as a simple integer
argument which was argued would be clearer. I'm not particularly
opinionated about this if it really helps or not. The struct nsset itself
already contains the flags field since its name already indicates that it
can contain information required by different namespaces. None of this
should have functional consequences.

Signed-off-by: Christian Brauner 
Reviewed-by: Serge Hallyn 
Cc: Eric W. Biederman 
Cc: Serge Hallyn 
Cc: Jann Horn 
Cc: Michael Kerrisk 
Cc: Aleksa Sarai 
Link: https://lore.kernel.org/r/20200505140432.181565-2-christian.brauner@ubuntu.com

proc, time/namespace: Show clock symbolic names in /proc/pid/timens_offsets

2020-04-16T10:10:54+00:00

Michael Kerrisk suggested to replace numeric clock IDs with symbolic names.

Now the content of these files looks like this:
$ cat /proc/774/timens_offsets
monotonic      864000         0
boottime      1728000         0

For setting offsets, both representations of clocks (numeric and symbolic)
can be used.

As for compatibility, it is acceptable to change things as long as
userspace doesn't care. The format of timens_offsets files is very new and
there are no userspace tools yet which rely on this format.

But three projects crun, util-linux and criu rely on the interface of
setting time offsets and this is why it's required to continue supporting
the numeric clock IDs on write.

Fixes: 04a8682a71be ("fs/proc: Introduce /proc/pid/timens_offsets")
Suggested-by: Michael Kerrisk 
Signed-off-by: Andrei Vagin 
Signed-off-by: Thomas Gleixner 
Tested-by: Michael Kerrisk 
Acked-by: Michael Kerrisk 
Cc: Andrew Morton 
Cc: Eric W. Biederman 
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200411154031.642557-1-avagin@gmail.com

time/namespace: Fix time_for_children symlink

2020-04-07T10:37:21+00:00

Looking at the contents of the /proc/PID/ns/time_for_children symlink shows
an anomaly:

$ ls -l /proc/self/ns/* |awk '{print $9, $10, $11}'
...
/proc/self/ns/pid -> pid:[4026531836]
/proc/self/ns/pid_for_children -> pid:[4026531836]
/proc/self/ns/time -> time:[4026531834]
/proc/self/ns/time_for_children -> time_for_children:[4026531834]
/proc/self/ns/user -> user:[4026531837]
...

The reference for 'time_for_children' should be a 'time' namespace, just as
the reference for 'pid_for_children' is a 'pid' namespace.  In other words,
the above time_for_children link should read:

/proc/self/ns/time_for_children -> time:[4026531834]

Fixes: 769071ac9f20 ("ns: Introduce Time Namespace")
Signed-off-by: Michael Kerrisk 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Dmitry Safonov 
Acked-by: Christian Brauner 
Acked-by: Andrei Vagin 
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/a2418c48-ed80-3afe-116e-6611cb799557@gmail.com

lib/vdso: Move VCLOCK_TIMENS to vdso_clock_modes

2020-02-17T19:12:17+00:00

Move the time namespace indicator clock mode to the other ones for
consistency sake.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Vincenzo Frascino 
Link: https://lkml.kernel.org/r/20200207124403.656097274@linutronix.de

fs/proc: Introduce /proc/pid/timens_offsets

2020-01-14T11:20:59+00:00

API to set time namespace offsets for children processes, i.e.:
echo "$clockid $offset_sec $offset_nsec" > /proc/self/timens_offsets

Co-developed-by: Dmitry Safonov 
Signed-off-by: Andrei Vagin 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20191112012724.250792-28-dima@arista.com

x86/vdso: Zap vvar pages when switching to a time namespace

2020-01-14T11:20:59+00:00

The VVAR page layout depends on whether a task belongs to the root or
non-root time namespace. Whenever a task changes its namespace, the VVAR
page tables are cleared and then they will be re-faulted with a
corresponding layout.

Co-developed-by: Andrei Vagin 
Signed-off-by: Andrei Vagin 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20191112012724.250792-27-dima@arista.com

time: Allocate per-timens vvar page

2020-01-14T11:20:58+00:00

VDSO support for Time namespace needs to set up a page with the same
layout as VVAR. That timens page will be placed on position of VVAR page
inside namespace. That page contains time namespace clock offsets and it
has vdso_data->seq set to 1 to enforce the slow path and
vdso_data->clock_mode set to VCLOCK_TIMENS to enforce the time namespace
handling path.

Allocate the timens page during namespace creation. Setup the offsets
when the first task enters the ns and freeze them to guarantee the pace
of monotonic/boottime clocks and to avoid breakage of applications.

The design decision is to have a global offset_lock which is used during
namespace offsets setup and to freeze offsets when the first task joins the
new time namespace. That is better in terms of memory usage compared to
having a per namespace mutex that's used only during the setup period.

Suggested-by: Andy Lutomirski 
Based-on-work-by: Thomas Gleixner 
Co-developed-by: Andrei Vagin 
Signed-off-by: Andrei Vagin 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20191112012724.250792-24-dima@arista.com