[v4,0/6] landlock: Signal scoping support

Message

Tahera Fahimi Sept. 6, 2024, 9:30 p.m. UTC

This patch series adds scoping mechanism for signals.
Closes: https://github.com/landlock-lsm/linux/issues/8

Problem
=======

A sandboxed process is currently not restricted from sending signals
(e.g. SIGKILL) to processes outside the sandbox since Landlock has no
restriction on signals(see more details in [1]).

A simple way to apply this restriction would be to scope signals the
same way abstract unix sockets are restricted.

[1]https://lore.kernel.org/all/[e-mail]/

Solution
========

To solve this issue, we extend the "scoped" field in the Landlock
ruleset attribute structure by introducing "LANDLOCK_SCOPED_SIGNAL"
field to specify that a ruleset will deny sending any signals from
within the sandbox domain to its parent(i.e. any parent sandbox or
non-sandbox processes).

Example
=======

Create a sansboxed shell and pass the character "s" to LL_SCOPED:
LL_FD_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
Try to send a signal(like SIGTRAP) to a process ID <PID> through:
kill -SIGTRAP <PID>
The sandboxed process should not be able to send the signal.

Previous Versions
=================
v3:https://lore.kernel.org/all/[e-mail]/
v2:https://lore.kernel.org/all/[e-mail]/
v1:https://lore.kernel.org/all/[e-mail]/

Tahera Fahimi (6):
  landlock: Add signal scoping control
  selftest/landlock: Signal restriction tests
  selftest/landlock: Add signal_scoping_threads test
  selftest/landlock: Test file_send_sigiotask by sending out-of-bound
    message
  sample/landlock: Support sample for signal scoping restriction
  landlock: Document LANDLOCK_SCOPED_SIGNAL

 Documentation/userspace-api/landlock.rst      |  22 +-
 include/uapi/linux/landlock.h                 |   3 +
 samples/landlock/sandboxer.c                  |  17 +-
 security/landlock/fs.c                        |  17 +
 security/landlock/fs.h                        |   6 +
 security/landlock/limits.h                    |   2 +-
 security/landlock/task.c                      |  59 +++
 .../selftests/landlock/scoped_signal_test.c   | 371 ++++++++++++++++++
 .../testing/selftests/landlock/scoped_test.c  |   2 +-
 9 files changed, 486 insertions(+), 13 deletions(-)
 create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c

Comments

Mickaël Salaün Sept. 11, 2024, 6:17 p.m. UTC | #1

We should also have the same tests as for scoped_vs_unscoped variants.
I renamed them from the abstract unix socket patch series, please take a
look:
https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/log/?h=next

I'll send more reviews tomorrow and I'll fix most of them in my -next
branch (WIP), except for the hook_file_send_sigiotask tests and these
scoped_vs_unscoped variants that you should resolve.

On Fri, Sep 06, 2024 at 03:30:02PM -0600, Tahera Fahimi wrote:
> This patch series adds scoping mechanism for signals.
> Closes: https://github.com/landlock-lsm/linux/issues/8
> 
> Problem
> =======
> 
> A sandboxed process is currently not restricted from sending signals
> (e.g. SIGKILL) to processes outside the sandbox since Landlock has no
> restriction on signals(see more details in [1]).
> 
> A simple way to apply this restriction would be to scope signals the
> same way abstract unix sockets are restricted.
> 
> [1]https://lore.kernel.org/all/[e-mail]/
> 
> Solution
> ========
> 
> To solve this issue, we extend the "scoped" field in the Landlock
> ruleset attribute structure by introducing "LANDLOCK_SCOPED_SIGNAL"
> field to specify that a ruleset will deny sending any signals from
> within the sandbox domain to its parent(i.e. any parent sandbox or
> non-sandbox processes).
> 
> Example
> =======
> 
> Create a sansboxed shell and pass the character "s" to LL_SCOPED:
> LL_FD_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
> Try to send a signal(like SIGTRAP) to a process ID <PID> through:
> kill -SIGTRAP <PID>
> The sandboxed process should not be able to send the signal.
> 
> Previous Versions
> =================
> v3:https://lore.kernel.org/all/[e-mail]/
> v2:https://lore.kernel.org/all/[e-mail]/
> v1:https://lore.kernel.org/all/[e-mail]/
> 
> Tahera Fahimi (6):
>   landlock: Add signal scoping control
>   selftest/landlock: Signal restriction tests
>   selftest/landlock: Add signal_scoping_threads test
>   selftest/landlock: Test file_send_sigiotask by sending out-of-bound
>     message
>   sample/landlock: Support sample for signal scoping restriction
>   landlock: Document LANDLOCK_SCOPED_SIGNAL
> 
>  Documentation/userspace-api/landlock.rst      |  22 +-
>  include/uapi/linux/landlock.h                 |   3 +
>  samples/landlock/sandboxer.c                  |  17 +-
>  security/landlock/fs.c                        |  17 +
>  security/landlock/fs.h                        |   6 +
>  security/landlock/limits.h                    |   2 +-
>  security/landlock/task.c                      |  59 +++
>  .../selftests/landlock/scoped_signal_test.c   | 371 ++++++++++++++++++
>  .../testing/selftests/landlock/scoped_test.c  |   2 +-
>  9 files changed, 486 insertions(+), 13 deletions(-)
>  create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c
> 
> -- 
> 2.34.1
>

Tahera Fahimi Sept. 12, 2024, 12:15 a.m. UTC | #2

On Wed, Sep 11, 2024 at 08:17:04PM +0200, Mickaël Salaün wrote:
> We should also have the same tests as for scoped_vs_unscoped variants.
Hi, 

Thanks for the review, I will add them soon.
> I renamed them from the abstract unix socket patch series, please take a
> look:
> https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/log/?h=next
Wonderful! Thank you :)

> I'll send more reviews tomorrow and I'll fix most of them in my -next
> branch (WIP), except for the hook_file_send_sigiotask tests and these
> scoped_vs_unscoped variants that you should resolve.
I will keep an eye on reviews. What parts of hook_file_send_sigiotask
would need changes?

> On Fri, Sep 06, 2024 at 03:30:02PM -0600, Tahera Fahimi wrote:
> > This patch series adds scoping mechanism for signals.
> > Closes: https://github.com/landlock-lsm/linux/issues/8
> > 
> > Problem
> > =======
> > 
> > A sandboxed process is currently not restricted from sending signals
> > (e.g. SIGKILL) to processes outside the sandbox since Landlock has no
> > restriction on signals(see more details in [1]).
> > 
> > A simple way to apply this restriction would be to scope signals the
> > same way abstract unix sockets are restricted.
> > 
> > [1]https://lore.kernel.org/all/[e-mail]/
> > 
> > Solution
> > ========
> > 
> > To solve this issue, we extend the "scoped" field in the Landlock
> > ruleset attribute structure by introducing "LANDLOCK_SCOPED_SIGNAL"
> > field to specify that a ruleset will deny sending any signals from
> > within the sandbox domain to its parent(i.e. any parent sandbox or
> > non-sandbox processes).
> > 
> > Example
> > =======
> > 
> > Create a sansboxed shell and pass the character "s" to LL_SCOPED:
> > LL_FD_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
> > Try to send a signal(like SIGTRAP) to a process ID <PID> through:
> > kill -SIGTRAP <PID>
> > The sandboxed process should not be able to send the signal.
> > 
> > Previous Versions
> > =================
> > v3:https://lore.kernel.org/all/[e-mail]/
> > v2:https://lore.kernel.org/all/[e-mail]/
> > v1:https://lore.kernel.org/all/[e-mail]/
> > 
> > Tahera Fahimi (6):
> >   landlock: Add signal scoping control
> >   selftest/landlock: Signal restriction tests
> >   selftest/landlock: Add signal_scoping_threads test
> >   selftest/landlock: Test file_send_sigiotask by sending out-of-bound
> >     message
> >   sample/landlock: Support sample for signal scoping restriction
> >   landlock: Document LANDLOCK_SCOPED_SIGNAL
> > 
> >  Documentation/userspace-api/landlock.rst      |  22 +-
> >  include/uapi/linux/landlock.h                 |   3 +
> >  samples/landlock/sandboxer.c                  |  17 +-
> >  security/landlock/fs.c                        |  17 +
> >  security/landlock/fs.h                        |   6 +
> >  security/landlock/limits.h                    |   2 +-
> >  security/landlock/task.c                      |  59 +++
> >  .../selftests/landlock/scoped_signal_test.c   | 371 ++++++++++++++++++
> >  .../testing/selftests/landlock/scoped_test.c  |   2 +-
> >  9 files changed, 486 insertions(+), 13 deletions(-)
> >  create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c
> > 
> > -- 
> > 2.34.1
> >

Mickaël Salaün Sept. 12, 2024, 12:51 p.m. UTC | #3

On Wed, Sep 11, 2024 at 06:15:24PM -0600, Tahera Fahimi wrote:
> On Wed, Sep 11, 2024 at 08:17:04PM +0200, Mickaël Salaün wrote:
> > We should also have the same tests as for scoped_vs_unscoped variants.
> Hi, 
> 
> Thanks for the review, I will add them soon.
> > I renamed them from the abstract unix socket patch series, please take a
> > look:
> > https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/log/?h=next
> Wonderful! Thank you :)
> 
> > I'll send more reviews tomorrow and I'll fix most of them in my -next
> > branch (WIP), except for the hook_file_send_sigiotask tests and these
> > scoped_vs_unscoped variants that you should resolve.
> I will keep an eye on reviews. What parts of hook_file_send_sigiotask
> would need changes?

The file_send_sigiotask hook was not fully covered.  It's OK now, I
reworked this test to fix that with four variants.

You still need to work on the scoped_vs_unscoped tests for signaling
though.

> 
> > On Fri, Sep 06, 2024 at 03:30:02PM -0600, Tahera Fahimi wrote:
> > > This patch series adds scoping mechanism for signals.
> > > Closes: https://github.com/landlock-lsm/linux/issues/8
> > > 
> > > Problem
> > > =======
> > > 
> > > A sandboxed process is currently not restricted from sending signals
> > > (e.g. SIGKILL) to processes outside the sandbox since Landlock has no
> > > restriction on signals(see more details in [1]).
> > > 
> > > A simple way to apply this restriction would be to scope signals the
> > > same way abstract unix sockets are restricted.
> > > 
> > > [1]https://lore.kernel.org/all/[e-mail]/
> > > 
> > > Solution
> > > ========
> > > 
> > > To solve this issue, we extend the "scoped" field in the Landlock
> > > ruleset attribute structure by introducing "LANDLOCK_SCOPED_SIGNAL"
> > > field to specify that a ruleset will deny sending any signals from
> > > within the sandbox domain to its parent(i.e. any parent sandbox or
> > > non-sandbox processes).
> > > 
> > > Example
> > > =======
> > > 
> > > Create a sansboxed shell and pass the character "s" to LL_SCOPED:
> > > LL_FD_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
> > > Try to send a signal(like SIGTRAP) to a process ID <PID> through:
> > > kill -SIGTRAP <PID>
> > > The sandboxed process should not be able to send the signal.
> > > 
> > > Previous Versions
> > > =================
> > > v3:https://lore.kernel.org/all/[e-mail]/
> > > v2:https://lore.kernel.org/all/[e-mail]/
> > > v1:https://lore.kernel.org/all/[e-mail]/
> > > 
> > > Tahera Fahimi (6):
> > >   landlock: Add signal scoping control
> > >   selftest/landlock: Signal restriction tests
> > >   selftest/landlock: Add signal_scoping_threads test
> > >   selftest/landlock: Test file_send_sigiotask by sending out-of-bound
> > >     message
> > >   sample/landlock: Support sample for signal scoping restriction
> > >   landlock: Document LANDLOCK_SCOPED_SIGNAL
> > > 
> > >  Documentation/userspace-api/landlock.rst      |  22 +-
> > >  include/uapi/linux/landlock.h                 |   3 +
> > >  samples/landlock/sandboxer.c                  |  17 +-
> > >  security/landlock/fs.c                        |  17 +
> > >  security/landlock/fs.h                        |   6 +
> > >  security/landlock/limits.h                    |   2 +-
> > >  security/landlock/task.c                      |  59 +++
> > >  .../selftests/landlock/scoped_signal_test.c   | 371 ++++++++++++++++++
> > >  .../testing/selftests/landlock/scoped_test.c  |   2 +-
> > >  9 files changed, 486 insertions(+), 13 deletions(-)
> > >  create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c
> > > 
> > > -- 
> > > 2.34.1
> > > 
> 
>