linux-toradex.git/kernel/pid.c, branch v5.17-rc4

pid: add pidfd_get_task() helper

2021-10-14T11:29:18+00:00

The number of system calls making use of pidfds is constantly
increasing. Some of those new system calls duplicate the code to turn a
pidfd into task_struct it refers to. Give them a simple helper for this.

Link: https://lore.kernel.org/r/20211004125050.1153693-2-christian.brauner@ubuntu.com
Link: https://lore.kernel.org/r/20211011133245.1703103-2-brauner@kernel.org
Cc: Vlastimil Babka 
Cc: Suren Baghdasaryan 
Cc: Matthew Bobrowski 
Cc: Alexander Duyck 
Cc: David Hildenbrand 
Cc: Jan Kara 
Cc: Minchan Kim 
Reviewed-by: Matthew Bobrowski 
Acked-by: David Hildenbrand 
Signed-off-by: Christian Brauner

kernel/pid.c: implement additional checks upon pidfd_create() parameters

2021-08-10T10:53:07+00:00

By adding the pidfd_create() declaration to linux/pid.h, we
effectively expose this function to the rest of the kernel. In order
to avoid any unintended behavior, or set false expectations upon this
function, ensure that constraints are forced upon each of the passed
parameters. This includes the checking of whether the passed struct
pid is a thread-group leader as pidfd creation is currently limited to
such pid types.

Link: https://lore.kernel.org/r/2e9b91c2d529d52a003b8b86c45f866153be9eb5.1628398044.git.repnop@google.com
Signed-off-by: Matthew Bobrowski 
Acked-by: Christian Brauner 
Signed-off-by: Jan Kara

kernel/pid.c: remove static qualifier from pidfd_create()

2021-08-10T10:53:04+00:00

With the idea of returning pidfds from the fanotify API, we need to
expose a mechanism for creating pidfds. We drop the static qualifier
from pidfd_create() and add its declaration to linux/pid.h so that the
pidfd_create() helper can be called from other kernel subsystems
i.e. fanotify.

Link: https://lore.kernel.org/r/0c68653ec32f1b7143301f0231f7ed14062fd82b.1628398044.git.repnop@google.com
Signed-off-by: Matthew Bobrowski 
Acked-by: Christian Brauner 
Signed-off-by: Jan Kara

Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2020-12-16T03:36:48+00:00

Pull exec-update-lock update from Eric Biederman:
 "The key point of this is to transform exec_update_mutex into a
  rw_semaphore so readers can be separated from writers.

  This makes it easier to understand what the holders of the lock are
  doing, and makes it harder to contend or deadlock on the lock.

  The real deadlock fix wound up in perf_event_open"

* 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  exec: Transform exec_update_mutex into a rw_semaphore

Merge tag 'fixes-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2020-12-15T00:40:27+00:00

Pull misc fixes from Christian Brauner:
 "This contains several fixes which felt worth being combined into a
  single branch:

   - Use put_nsproxy() instead of open-coding it switch_task_namespaces()

   - Kirill's work to unify lifecycle management for all namespaces. The
     lifetime counters are used identically for all namespaces types.
     Namespaces may of course have additional unrelated counters and
     these are not altered. This work allows us to unify the type of the
     counters and reduces maintenance cost by moving the counter in one
     place and indicating that basic lifetime management is identical
     for all namespaces.

   - Peilin's fix adding three byte padding to Dmitry's
     PTRACE_GET_SYSCALL_INFO uapi struct to prevent an info leak.

   - Two smal patches to convert from the /* fall through */ comment
     annotation to the fallthrough keyword annotation which I had taken
     into my branch and into -next before df561f6688fe ("treewide: Use
     fallthrough pseudo-keyword") made it upstream which fixed this
     tree-wide.

     Since I didn't want to invalidate all testing for other commits I
     didn't rebase and kept them"

* tag 'fixes-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  nsproxy: use put_nsproxy() in switch_task_namespaces()
  sys: Convert to the new fallthrough notation
  signal: Convert to the new fallthrough notation
  time: Use generic ns_common::count
  cgroup: Use generic ns_common::count
  mnt: Use generic ns_common::count
  user: Use generic ns_common::count
  pid: Use generic ns_common::count
  ipc: Use generic ns_common::count
  uts: Use generic ns_common::count
  net: Use generic ns_common::count
  ns: Add a common refcount into ns_common
  ptrace: Prevent kernel-infoleak in ptrace_get_syscall_info()

exec: Transform exec_update_mutex into a rw_semaphore

2020-12-10T19:13:32+00:00

Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.  The problematic lock ordering found by lockdep
was:

   perf_event_open  (exec_update_mutex -> ovl_i_mutex)
   chown            (ovl_i_mutex       -> sb_writes)
   sendfile         (sb_writes         -> p->lock)
     by reading from a proc file and writing to overlayfs
   proc_pid_syscall (p->lock           -> exec_update_mutex)

While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same.  They are all readers.  The only writer is
exec.

There is no reason for readers to block on each other.  So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.

Cc: Jann Horn 
Cc: Vasiliy Kulikov 
Cc: Al Viro 
Cc: Bernd Edlinger 
Cc: Oleg Nesterov 
Cc: Christopher Yeoh 
Cc: Cyrill Gorcunov 
Cc: Sargun Dhillon 
Cc: Christian Brauner 
Cc: Arnd Bergmann 
Cc: Peter Zijlstra 
Cc: Ingo Molnar 
Cc: Arnaldo Carvalho de Melo 
Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman

pid: move pidfd_get_pid() to pid.c

2020-10-18T16:27:10+00:00

process_madvise syscall needs pidfd_get_pid function to translate pidfd to
pid so this patch move the function to kernel/pid.c.

Suggested-by: Alexander Duyck 
Signed-off-by: Minchan Kim 
Signed-off-by: Andrew Morton 
Reviewed-by: Suren Baghdasaryan 
Reviewed-by: Alexander Duyck 
Reviewed-by: Vlastimil Babka 
Acked-by: Christian Brauner 
Acked-by: David Rientjes 
Cc: Jens Axboe 
Cc: Jann Horn 
Cc: Brian Geffon 
Cc: Daniel Colascione 
Cc: Joel Fernandes 
Cc: Johannes Weiner 
Cc: John Dias 
Cc: Kirill Tkhai 
Cc: Michal Hocko 
Cc: Oleksandr Natalenko 
Cc: Sandeep Patil 
Cc: SeongJae Park 
Cc: SeongJae Park 
Cc: Shakeel Butt 
Cc: Sonny Rao 
Cc: Tim Murray 
Cc: Christian Brauner 
Cc: Florian Weimer 
Cc: 
Link: http://lkml.kernel.org/r/20200302193630.68771-5-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200622192900.22757-3-minchan@kernel.org
Link: https://lkml.kernel.org/r/20200901000633.1920247-3-minchan@kernel.org
Signed-off-by: Linus Torvalds

pidfd: support PIDFD_NONBLOCK in pidfd_open()

2020-09-04T10:34:50+00:00

Introduce PIDFD_NONBLOCK to support non-blocking pidfd file descriptors.

Ever since the introduction of pidfds and more advanced async io various
programming languages such as Rust have grown support for async event
libraries. These libraries are created to help build epoll-based event loops
around file descriptors. A common pattern is to automatically make all file
descriptors they manage to O_NONBLOCK.

For such libraries the EAGAIN error code is treated specially. When a function
is called that returns EAGAIN the function isn't called again until the event
loop indicates the the file descriptor is ready. Supporting EAGAIN when
waiting on pidfds makes such libraries just work with little effort. In the
following patch we will extend waitid() internally to support non-blocking
pidfds.

This introduces a new flag PIDFD_NONBLOCK that is equivalent to O_NONBLOCK.
This follows the same patterns we have for other (anon inode) file descriptors
such as EFD_NONBLOCK, IN_NONBLOCK, SFD_NONBLOCK, TFD_NONBLOCK and the same for
close-on-exec flags.

Suggested-by: Josh Triplett 
Signed-off-by: Christian Brauner 
Reviewed-by: Josh Triplett 
Reviewed-by: Oleg Nesterov 
Cc: Kees Cook 
Cc: Sargun Dhillon 
Cc: Oleg Nesterov 
Link: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/
Link: https://github.com/joshtriplett/async-pidfd
Link: https://lore.kernel.org/r/20200902102130.147672-2-christian.brauner@ubuntu.com

pid: Use generic ns_common::count

2020-08-19T12:14:06+00:00

Switch over pid namespaces to use the newly introduced common lifetime
counter.

Currently every namespace type has its own lifetime counter which is stored
in the specific namespace struct. The lifetime counters are used
identically for all namespaces types. Namespaces may of course have
additional unrelated counters and these are not altered.

This introduces a common lifetime counter into struct ns_common. The
ns_common struct encompasses information that all namespaces share. That
should include the lifetime counter since its common for all of them.

It also allows us to unify the type of the counters across all namespaces.
Most of them use refcount_t but one uses atomic_t and at least one uses
kref. Especially the last one doesn't make much sense since it's just a
wrapper around refcount_t since 2016 and actually complicates cleanup
operations by having to use container_of() to cast the correct namespace
struct out of struct ns_common.

Having the lifetime counter for the namespaces in one place reduces
maintenance cost. Not just because after switching all namespaces over we
will have removed more code than we added but also because the logic is
more easily understandable and we indicate to the user that the basic
lifetime requirements for all namespaces are currently identical.

Signed-off-by: Kirill Tkhai 
Reviewed-by: Kees Cook 
Acked-by: Christian Brauner 
Link: https://lore.kernel.org/r/159644979226.604812.7512601754841882036.stgit@localhost.localdomain
Signed-off-by: Christian Brauner

Merge tag 'cap-checkpoint-restore-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2020-08-04T22:02:07+00:00

Pull checkpoint-restore updates from Christian Brauner:
"This enables unprivileged checkpoint/restore of processes.

Given that this work has been going on for quite some time the first
sentence in this summary is hopefully more exciting than the actual
final code changes required. Unprivileged checkpoint/restore has seen
a frequent increase in interest over the last two years and has thus
been one of the main topics for the combined containers &
checkpoint/restore microconference since at least 2018 (cf. [1]).

Here are just the three most frequent use-cases that were brought forward:

- The JVM developers are integrating checkpoint/restore into a Java
VM to significantly decrease the startup time.

- In high-performance computing environment a resource manager will
typically be distributing jobs where users are always running as
non-root. Long-running and "large" processes with significant
startup times are supposed to be checkpointed and restored with
CRIU.

- Container migration as a non-root user.

In all of these scenarios it is either desirable or required to run
without CAP_SYS_ADMIN. The userspace implementation of
checkpoint/restore CRIU already has the pull request for supporting
unprivileged checkpoint/restore up (cf. [2]).

To enable unprivileged checkpoint/restore a new dedicated capability
CAP_CHECKPOINT_RESTORE is introduced. This solution has last been
discussed in 2019 in a talk by Google at Linux Plumbers (cf. [1]
"Update on Task Migration at Google Using CRIU") with Adrian and
Nicolas providing the implementation now over the last months. In
essence, this allows the CRIU binary to be installed with the
CAP_CHECKPOINT_RESTORE vfs capability set thereby enabling
unprivileged users to restore processes.

To make this possible the following permissions are altered:

- Selecting a specific PID via clone3() set_tid relaxed from userns
CAP_SYS_ADMIN to CAP_CHECKPOINT_RESTORE.

- Selecting a specific PID via /proc/sys/kernel/ns_last_pid relaxed
from userns CAP_SYS_ADMIN to CAP_CHECKPOINT_RESTORE.

- Accessing /proc/pid/map_files relaxed from init userns
CAP_SYS_ADMIN to init userns CAP_CHECKPOINT_RESTORE.

- Changing /proc/self/exe from userns CAP_SYS_ADMIN to userns
CAP_CHECKPOINT_RESTORE.

Of these four changes the /proc/self/exe change deserves a few words
because the reasoning behind even restricting /proc/self/exe changes
in the first place is just full of historical quirks and tracking this
down was a questionable version of fun that I'd like to spare others.

In short, it is trivial to change /proc/self/exe as an unprivileged
user, i.e. without userns CAP_SYS_ADMIN right now. Either via ptrace()
or by simply intercepting the elf loader in userspace during exec.
Nicolas was nice enough to even provide a POC for the latter (cf. [3])
to illustrate this fact.

The original patchset which introduced PR_SET_MM_MAP had no
permissions around changing the exe link. They too argued that it is
trivial to spoof the exe link already which is true. The argument
brought up against this was that the Tomoyo LSM uses the exe link in
tomoyo_manager() to detect whether the calling process is a policy
manager. This caused changing the exe links to be guarded by userns
CAP_SYS_ADMIN.

All in all this rather seems like a "better guard it with something
rather than nothing" argument which imho doesn't qualify as a great
security policy. Again, because spoofing the exe link is possible for
the calling process so even if this were security relevant it was
broken back then and would be broken today. So technically, dropping
all permissions around changing the exe link would probably be
possible and would send a clearer message to any userspace that relies
on /proc/self/exe for security reasons that they should stop doing
this but for now we're only relaxing the exe link permissions from
userns CAP_SYS_ADMIN to userns CAP_CHECKPOINT_RESTORE.

There's a final uapi change in here. Changing the exe link used to
accidently return EINVAL when the caller lacked the necessary
permissions instead of the more correct EPERM. This pr contains a
commit fixing this. I assume that userspace won't notice or care and
if they do I will revert this commit. But since we are changing the
permissions anyway it seems like a good opportunity to try this fix.

With these changes merged unprivileged checkpoint/restore will be
possible and has already been tested by various users"

[1] LPC 2018
1. "Task Migration at Google Using CRIU"
https://www.youtube.com/watch?v=yI_1cuhoDgA&t=12095
2. "Securely Migrating Untrusted Workloads with CRIU"
https://www.youtube.com/watch?v=yI_1cuhoDgA&t=14400
LPC 2019
1. "CRIU and the PID dance"
https://www.youtube.com/watch?v=LN2CUgp8deo&list=PLVsQ_xZBEyN30ZA3Pc9MZMFzdjwyz26dO&index=9&t=2m48s
2. "Update on Task Migration at Google Using CRIU"
https://www.youtube.com/watch?v=LN2CUgp8deo&list=PLVsQ_xZBEyN30ZA3Pc9MZMFzdjwyz26dO&index=9&t=1h2m8s

[2] https://github.com/checkpoint-restore/criu/pull/1155

[3] https://github.com/nviennot/run_as_exe

* tag 'cap-checkpoint-restore-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
selftests: add clone3() CAP_CHECKPOINT_RESTORE test
prctl: exe link permission error changed from -EINVAL to -EPERM
prctl: Allow local CAP_CHECKPOINT_RESTORE to change /proc/self/exe
proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE
pid_namespace: use checkpoint_restore_ns_capable() for ns_last_pid
pid: use checkpoint_restore_ns_capable() for set_tid
capabilities: Introduce CAP_CHECKPOINT_RESTORE