Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 21 Feb 2017 21:21:21 -0800 | Subject | Re: [PATCH v5 10/10] landlock: Add user and kernel documentation for Landlock |
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On Tue, Feb 21, 2017 at 5:26 PM, Mickaël Salaün <mic@digikod.net> wrote: > This documentation can be built with the Sphinx framework. > > Signed-off-by: Mickaël Salaün <mic@digikod.net> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Andy Lutomirski <luto@amacapital.net> > Cc: Daniel Borkmann <daniel@iogearbox.net> > Cc: David S. Miller <davem@davemloft.net> > Cc: James Morris <james.l.morris@oracle.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Kees Cook <keescook@chromium.org> > Cc: Serge E. Hallyn <serge@hallyn.com>
> + > +Writing a rule > +-------------- > + > +To enforce a security policy, a thread first needs to create a Landlock rule. > +The easiest way to write an eBPF program depicting a security rule is to write > +it in the C language. As described in *samples/bpf/README.rst*, LLVM can > +compile such programs. Files *samples/bpf/landlock1_kern.c* and those in > +*tools/testing/selftests/landlock/rules/* can be used as examples. The > +following example is a simple rule to forbid file creation, whatever syscall > +may be used (e.g. open, mkdir, link...). > + > +.. code-block:: c > + > + static int deny_file_creation(struct landlock_context *ctx) > + { > + if (ctx->arg2 & LANDLOCK_ACTION_FS_NEW) > + return 1; > + return 0; > + } > +
Would it make sense to define landlock_context (or at least a prefix thereof) in here? Also, can't "arg2" have a better name?
Can you specify what the return value means? Are 0 and 1 the only choices? Would "KILL" be useful? How about "COREDUMP"?
> +File system action types > +------------------------ > + > +Flags are used to express actions. This makes it possible to compose actions > +and leaves room for future improvements to add more fine-grained action types. > + > +.. kernel-doc:: include/uapi/linux/bpf.h > + :doc: landlock_action_fs > + > +.. flat-table:: FS action types availability > + > + * - flags > + - since > + > + * - LANDLOCK_ACTION_FS_EXEC > + - v1 > + > + * - LANDLOCK_ACTION_FS_WRITE > + - v1 > + > + * - LANDLOCK_ACTION_FS_READ > + - v1 > + > + * - LANDLOCK_ACTION_FS_NEW > + - v1 > + > + * - LANDLOCK_ACTION_FS_GET > + - v1 > + > + * - LANDLOCK_ACTION_FS_REMOVE > + - v1 > + > + * - LANDLOCK_ACTION_FS_IOCTL > + - v1 > + > + * - LANDLOCK_ACTION_FS_LOCK > + - v1 > + > + * - LANDLOCK_ACTION_FS_FCNTL > + - v1
What happens if you run an old program on a new kernel? Can you get unexpected action types?
> + > + > +Ability types > +------------- > + > +The ability of a Landlock rule describes the available features (i.e. context > +fields and helpers). This is useful to abstract user-space privileges for > +Landlock rules, which may not need all abilities (e.g. debug). Only the > +minimal set of abilities should be used (e.g. disable debug once in > +production). > + > + > +.. kernel-doc:: include/uapi/linux/bpf.h > + :doc: landlock_subtype_ability > + > +.. flat-table:: Ability types availability > + > + * - flags > + - since > + - capability > + > + * - LANDLOCK_SUBTYPE_ABILITY_WRITE > + - v1 > + - CAP_SYS_ADMIN > + > + * - LANDLOCK_SUBTYPE_ABILITY_DEBUG > + - v1 > + - CAP_SYS_ADMIN > +
What do "WRITE" and "DEBUG" mean in this context? I'm totally lost.
Hmm. Reading below, "WRITE" seems to mean "modify state". Would that be accurate?
> + > +Helper functions > +---------------- > + > +See *include/uapi/linux/bpf.h* for functions documentation. > + > +.. flat-table:: Generic functions availability > +
> + > + * - bpf_get_current_comm > + - v1 > + - LANDLOCK_SUBTYPE_ABILITY_DEBUG
What would this be used for?
> + * - bpf_get_trace_printk > + - v1 > + - LANDLOCK_SUBTYPE_ABILITY_DEBUG > +
This is different from the other DEBUG stuff in that it has side effects. I wonder if it should have a different flag.
--Andy
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