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Re: [RFC v2 06/10] landlock: Add LSM hooks

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On Aug 25, 2016 12:34 PM, "Mickaël Salaün" <mic@digikod.net> wrote:
>
> Add LSM hooks which can be used by userland through Landlock (eBPF)
> programs. This programs are limited to a whitelist of functions (cf.
> next commit). The eBPF program context is depicted by the struct
> landlock_data (cf. include/uapi/linux/bpf.h):
> * hook: LSM hook ID (useful when using the same program for multiple LSM
>   hooks);
> * cookie: the 16-bit value from the seccomp filter that triggered this
>   Landlock program;
> * args[6]: array of LSM hook arguments.
>
> The LSM hook arguments can contain raw values as integers or
> (unleakable) pointers. The only way to use the pointers are to pass them
> to an eBPF function according to their types (e.g. the
> bpf_landlock_cmp_fs_beneath_with_struct_file function can use a struct
> file pointer).
>
> For now, there is three hooks for file system access control:
> * file_open;
> * file_permission;
> * mmap_file.
>

What's the purpose of exposing struct cred * to userspace?  It's
primarily just an optimization to save a bit of RAM, and it's a
dubious optimization at that.  What are you using it for?  Would it
make more sense to use struct task_struct * or struct pid * instead?

Also, exposing struct cred * has a really weird side-effect: it allows
(maybe even encourages) checking for pointer equality between two
struct cred * objects.  Doing so will have erratic results.

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[RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
  [RFC v2 10/10] samples/landlock: Add sandbox example Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
  [RFC v2 05/10] seccomp: Handle Landlock Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
  [RFC v2 02/10] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
  [RFC v2 08/10] landlock: Handle file system comparisons Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
    Re: [RFC v2 08/10] landlock: Handle file system comparisons Andy Lutomirski <luto@amacapital.net> - 2016-08-25 13:20 +0200
      Re: [RFC v2 08/10] landlock: Handle file system comparisons Mickaël Salaün <mic@digikod.net> - 2016-08-25 16:20 +0200
        Re: [RFC v2 08/10] landlock: Handle file system comparisons Andy Lutomirski <luto@amacapital.net> - 2016-08-26 17:00 +0200
          Re: [RFC v2 08/10] landlock: Handle file system comparisons Mickaël Salaün <mic@digikod.net> - 2016-08-27 15:50 +0200
  [RFC v2 01/10] landlock: Add Kconfig Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
  [RFC v2 07/10] landlock: Add errno check Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
    Re: [RFC v2 07/10] landlock: Add errno check Andy Lutomirski <luto@amacapital.net> - 2016-08-25 13:20 +0200
  [RFC v2 06/10] landlock: Add LSM hooks Mickaël Salaün <mic@digikod.net> - 2016-08-25 12:50 +0200
    Re: [RFC v2 06/10] landlock: Add LSM hooks Andy Lutomirski <luto@amacapital.net> - 2016-08-30 21:00 +0200
      Re: [RFC v2 06/10] landlock: Add LSM hooks Mickaël Salaün <mic@digikod.net> - 2016-08-30 22:20 +0200
        Re: [RFC v2 06/10] landlock: Add LSM hooks Andy Lutomirski <luto@amacapital.net> - 2016-08-30 22:20 +0200
          Re: [RFC v2 06/10] landlock: Add LSM hooks Mickaël Salaün <mic@digikod.net> - 2016-08-30 22:30 +0200
  Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski <luto@amacapital.net> - 2016-08-25 13:30 +0200
    Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün <mic@digikod.net> - 2016-08-25 16:00 +0200
  Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski <luto@amacapital.net> - 2016-08-27 09:50 +0200
    Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün <mic@digikod.net> - 2016-08-27 17:20 +0200
      Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing (cgroup  delegation) Mickaël Salaün <mic@digikod.net> - 2016-08-27 17:30 +0200
  Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski <luto@amacapital.net> - 2016-08-30 18:10 +0200
    Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski <luto@amacapital.net> - 2016-08-30 22:00 +0200
    Re: [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün <mic@digikod.net> - 2016-08-30 22:00 +0200

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