On 5/24/2023 9:02 AM, Mickaël Salaün wrote:

On 24/05/2023 17:38, Mickaël Salaün wrote:

quoted

On 23/05/2023 23:12, Paul Moore wrote:

quoted

On Tue, May 23, 2023 at 2:13 AM Jeff Xu [off-list ref] wrote:

quoted

On Mon, May 22, 2023 at 12:56 PM Paul Moore [off-list ref]
wrote:

quoted

On Thu, May 18, 2023 at 5:26 PM Casey Schaufler
[off-list ref] wrote:

quoted

On 5/18/2023 1:45 PM, Shervin Oloumi wrote:

quoted

Adds a new getprocattr hook function to the Landlock LSM, which
tracks
the landlocked state of the process. This is invoked when
user-space
reads /proc/[pid]/attr/domain

Please don't add a Landlock specific entry directly in the attr/
directory. Add it only to attr/landlock.

Also be aware that the LSM maintainer (Paul Moore) wants to move
away from the /proc/.../attr interfaces in favor of a new system
call,
which is in review.

What Casey said above.

There is still some uncertainty around timing, and if we're perfectly
honest, acceptance of the new syscalls at the Linus level, but yes, I
would very much like to see the LSM infrastructure move away from
procfs and towards a syscall API.  Part of the reasoning is that the
current procfs API is ill-suited to handle the multiple, stacked LSMs
and the other part being the complexity of procfs in a namespaced
system.  If the syscall API is ultimately rejected, we will need to
revisit the idea of a procfs API, but even then I think we'll need to
make some changes to the current approach.

As I believe we are in the latter stages of review for the syscall
API, perhaps you could take a look and ensure that the current
proposed API works for what you are envisioning with Landlock?

I agree, and since the LSM syscalls are almost ready that should not
change much the timing. In fact, extending these syscalls might be
easier than tweaking the current procfs/attr API for Landlock specific
requirements (e.g. scoped visibility). We should ensure that these
syscalls would be a good fit to return file descriptors, but in the
short term we only need to know if a process is landlocked or not, so a
raw return value (0 or -errno) will be enough.

Mentioning in the LSM syscalls patch series that they may deal with (and
return) file descriptors could help API reviewers though.

It should be kept in mind that the current LSM syscalls only deal with
the calling task, whereas the goal of this Landlock patch series is to
inspect other tasks. A new LSM syscall would need to be created to
handle pidfd e.g., named lsm_get_proc_attr() or lsm_get_pid_attr().

I think it would be lsm_get_pid_attr(). Yes, it's the obvious next step.

I'm not sure if this should be a generic LSM syscall or a Landlock
syscall though. I have plan to handle processes other than the caller
(e.g. to restrict an existing process hierarchy), so thinking about a
Landlock-specific syscall could make sense.

To summarize, creating a new LSM syscall to deal with pidfd and to get
LSM process "status/attr" looks OK. However, Landlock-specific
syscalls to deal with Landlock specificities (e.g. ruleset or domain
file descriptor) make more sense.

Having one LSM-generic syscall to get minimal Landlock attributes
(i.e. mainly to know if a process is sandboxed), and another
Landlock-specific syscall to do more things (e.g. get the domain file
descriptor, restrict a task) seems reasonable. The second one would
overlap with the first one though. What do you think?

I find it difficult to think of a file descriptor as an attribute of
a process. To my (somewhat unorthodox) thinking a file descriptor is
a name for an object, not an attribute of the object. You can't access
an object by its attributes, but you can by its name. An attribute is
a description of the object. I'm perfectly happy with lsm_get_pid_attr()
returning an attribute that is a file descriptor if it describes the
process in some way, but not as a substitute for opening /proc/42.