Re: [PATCH v1 3/3] landlock: Fix documentation style

[Mickaël Salaün <mic@xxxxxxxxxxx>]

On 23/09/2022 23:18, Günther Noack wrote:
> On Fri, Sep 23, 2022 at 05:42:07PM +0200, Mickaël Salaün wrote:
> > It seems that all code should use double backquotes, which is also used
> > to convert "%" defines.  Let's use an homogeneous style and remove all
> > use of simple backquotes (which should only be used for emphasis).
> >
> > Cc: Günther Noack <gnoack3000@xxxxxxxxx>
> > Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20220923154207.3311629-4-mic@xxxxxxxxxxx
> > ---
> >   Documentation/security/landlock.rst      |  4 +--
> >   Documentation/userspace-api/landlock.rst | 25 ++++++++-------
> >   include/uapi/linux/landlock.h            | 10 +++---
> >   security/landlock/syscalls.c             | 40 ++++++++++++------------
> >   4 files changed, 40 insertions(+), 39 deletions(-)
> >
> > diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst
> > index cc9617f3175b..c0029d5d02eb 100644
> > --- a/Documentation/security/landlock.rst
> > +++ b/Documentation/security/landlock.rst
> > @@ -54,8 +54,8 @@ content of a listed inode.  Indeed, a file name is local to its parent
> >   directory, and an inode can be referenced by multiple file names thanks to
> >   (hard) links.  Being able to unlink a file only has a direct impact on the
> >   directory, not the unlinked inode.  This is the reason why
> > -`LANDLOCK_ACCESS_FS_REMOVE_FILE` or `LANDLOCK_ACCESS_FS_REFER` are not allowed
> > -to be tied to files but only to directories.
> > +``LANDLOCK_ACCESS_FS_REMOVE_FILE`` or ``LANDLOCK_ACCESS_FS_REFER`` are not
> > +allowed to be tied to files but only to directories.
> >   
> >   Tests
> >   =====
> > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
> > index 83bae71bf042..cec780c2f497 100644
> > --- a/Documentation/userspace-api/landlock.rst
> > +++ b/Documentation/userspace-api/landlock.rst
> > @@ -69,7 +69,7 @@ should try to protect users as much as possible whatever the kernel they are
> >   using.  To avoid binary enforcement (i.e. either all security features or
> >   none), we can leverage a dedicated Landlock command to get the current version
> >   of the Landlock ABI and adapt the handled accesses.  Let's check if we should
> > -remove the `LANDLOCK_ACCESS_FS_REFER` access right which is only supported
> > +remove the ``LANDLOCK_ACCESS_FS_REFER`` access right which is only supported
> >   starting with the second version of the ABI.
> >   
> >   .. code-block:: c
> > @@ -128,7 +128,7 @@ descriptor.
> >   It may also be required to create rules following the same logic as explained
> >   for the ruleset creation, by filtering access rights according to the Landlock
> >   ABI version.  In this example, this is not required because
> > -`LANDLOCK_ACCESS_FS_REFER` is not allowed by any rule.
> > +``LANDLOCK_ACCESS_FS_REFER`` is not allowed by any rule.
> >   
> >   We now have a ruleset with one rule allowing read access to ``/usr`` while
> >   denying all other handled accesses for the filesystem.  The next step is to
> > @@ -154,8 +154,8 @@ The current thread is now ready to sandbox itself with the ruleset.
> >       }
> >       close(ruleset_fd);
> >   
> > -If the `landlock_restrict_self` system call succeeds, the current thread is now
> > -restricted and this policy will be enforced on all its subsequently created
> > +If the ``landlock_restrict_self`` system call succeeds, the current thread is
> > +now restricted and this policy will be enforced on all its subsequently created
> >   children as well.  Once a thread is landlocked, there is no way to remove its
> >   security policy; only adding more restrictions is allowed.  These threads are
> >   now in a new Landlock domain, merge of their parent one (if any) with the new
> > @@ -175,7 +175,8 @@ depend on their location (i.e. parent directories).  This is particularly
> >   relevant when we want to allow linking or renaming.  Indeed, having consistent
> >   access rights per directory enables to change the location of such directory
> >   without relying on the destination directory access rights (except those that
> > -are required for this operation, see `LANDLOCK_ACCESS_FS_REFER` documentation).
> > +are required for this operation, see ``LANDLOCK_ACCESS_FS_REFER``
> > +documentation).
> >   Having self-sufficient hierarchies also helps to tighten the required access
> >   rights to the minimal set of data.  This also helps avoid sinkhole directories,
> >   i.e.  directories where data can be linked to but not linked from.  However,
> > @@ -259,7 +260,7 @@ Backward and forward compatibility
> >   
> >   Landlock is designed to be compatible with past and future versions of the
> >   kernel.  This is achieved thanks to the system call attributes and the
> > -associated bitflags, particularly the ruleset's `handled_access_fs`.  Making
> > +associated bitflags, particularly the ruleset's ``handled_access_fs``.  Making
> >   handled access right explicit enables the kernel and user space to have a clear
> >   contract with each other.  This is required to make sure sandboxing will not
> >   get stricter with a system update, which could break applications.
> > @@ -394,7 +395,7 @@ according to the potentially lost constraints.  To protect against privilege
> >   escalations through renaming or linking, and for the sake of simplicity,
> >   Landlock previously limited linking and renaming to the same directory.
> >   Starting with the Landlock ABI version 2, it is now possible to securely
> > -control renaming and linking thanks to the new `LANDLOCK_ACCESS_FS_REFER`
> > +control renaming and linking thanks to the new ``LANDLOCK_ACCESS_FS_REFER``
> >   access right.
> >   
> >   .. _kernel_support:
> > @@ -403,14 +404,14 @@ Kernel support
> >   ==============
> >   
> >   Landlock was first introduced in Linux 5.13 but it must be configured at build
> > -time with `CONFIG_SECURITY_LANDLOCK=y`.  Landlock must also be enabled at boot
> > +time with ``CONFIG_SECURITY_LANDLOCK=y``.  Landlock must also be enabled at boot
> >   time as the other security modules.  The list of security modules enabled by
> > -default is set with `CONFIG_LSM`.  The kernel configuration should then
> > -contains `CONFIG_LSM=landlock,[...]` with `[...]`  as the list of other
> > +default is set with ``CONFIG_LSM``.  The kernel configuration should then
> > +contains ``CONFIG_LSM=landlock,[...]`` with ``[...]``  as the list of other
> >   potentially useful security modules for the running system (see the
> > -`CONFIG_LSM` help).
> > +``CONFIG_LSM`` help).
> >   
> > -If the running kernel does not have `landlock` in `CONFIG_LSM`, then we can
> > +If the running kernel does not have ``landlock`` in ``CONFIG_LSM``, then we can
> >   still enable it by adding ``lsm=landlock,[...]`` to
> >   Documentation/admin-guide/kernel-parameters.rst thanks to the bootloader
> >   configuration.
> > diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
> > index 23df4e0e8ace..9c4bcc37a455 100644
> > --- a/include/uapi/linux/landlock.h
> > +++ b/include/uapi/linux/landlock.h
> > @@ -26,7 +26,7 @@ struct landlock_ruleset_attr {
> >   	 * Landlock filesystem access rights that are not part of
> >   	 * handled_access_fs are allowed.  This is needed for backward
> >   	 * compatibility reasons.  One exception is the
> > -	 * LANDLOCK_ACCESS_FS_REFER access right, which is always implicitly
> > +	 * %LANDLOCK_ACCESS_FS_REFER access right, which is always implicitly
>
> At the risk of asking a newbie question, why is this access right
> prefixed with % in this command, but most others are surrounded by
> double-backticks in other places?

The % command is only interpreted in code comments, but it in ignored in 
RST files. This translates to double-backticks though. It seems that % 
is more appropriate this way and it is also more readable. I only used 
`` when I couldn't use %.

Jonathan may have a better explanation.

> According to [1], % is used to denote a constant - should these
> LANDLOCK_ACCESS_FS* rights not all be showing up as constants?
>
> [1] https://docs.kernel.org/doc-guide/kernel-doc.html#highlights-and-cross-references
>
> Apart from this item, this change looks good.
>
> >   	 * handled, but must still be explicitly handled to add new rules with
> >   	 * this access right.
> >   	 */
> > @@ -128,11 +128,11 @@ struct landlock_path_beneath_attr {
> >    *   hierarchy must also always have the same or a superset of restrictions of
> >    *   the source hierarchy.  If it is not the case, or if the domain doesn't
> >    *   handle this access right, such actions are denied by default with errno
> > - *   set to EXDEV.  Linking also requires a LANDLOCK_ACCESS_FS_MAKE_* access
> > - *   right on the destination directory, and renaming also requires a
> > - *   LANDLOCK_ACCESS_FS_REMOVE_* access right on the source's (file or
> > + *   set to ``EXDEV``.  Linking also requires a ``LANDLOCK_ACCESS_FS_MAKE_*``
> > + *   access right on the destination directory, and renaming also requires a
> > + *   ``LANDLOCK_ACCESS_FS_REMOVE_*`` access right on the source's (file or
> >    *   directory) parent.  Otherwise, such actions are denied with errno set to
> > - *   EACCES.  The EACCES errno prevails over EXDEV to let user space
> > + *   ``EACCES``.  The ``EACCES`` errno prevails over ``EXDEV`` to let user space
> >    *   efficiently deal with an unrecoverable error.
> >    *
> >    * .. warning::
> > diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> > index 735a0865ea11..2ca0ccbd905a 100644
> > --- a/security/landlock/syscalls.c
> > +++ b/security/landlock/syscalls.c
> > @@ -149,10 +149,10 @@ static const struct file_operations ruleset_fops = {
> >    *
> >    * Possible returned errors are:
> >    *
> > - * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > - * - EINVAL: unknown @flags, or unknown access, or too small @size;
> > - * - E2BIG or EFAULT: @attr or @size inconsistencies;
> > - * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
> > + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > + * - %EINVAL: unknown @flags, or unknown access, or too small @size;
> > + * - %E2BIG or %EFAULT: @attr or @size inconsistencies;
> > + * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
> >    */
> >   SYSCALL_DEFINE3(landlock_create_ruleset,
> >   		const struct landlock_ruleset_attr __user *const, attr,
> > @@ -280,7 +280,7 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
> >    * @ruleset_fd: File descriptor tied to the ruleset that should be extended
> >    *		with the new rule.
> >    * @rule_type: Identify the structure type pointed to by @rule_attr (only
> > - *             LANDLOCK_RULE_PATH_BENEATH for now).
> > + *             %LANDLOCK_RULE_PATH_BENEATH for now).
> >    * @rule_attr: Pointer to a rule (only of type &struct
> >    *             landlock_path_beneath_attr for now).
> >    * @flags: Must be 0.
> > @@ -290,17 +290,17 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
> >    *
> >    * Possible returned errors are:
> >    *
> > - * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > - * - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
> > + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > + * - %EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
> >    *   &landlock_path_beneath_attr.allowed_access is not a subset of the
> >    *   ruleset handled accesses);
> > - * - ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
> > - * - EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
> > + * - %ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
> > + * - %EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
> >    *   member of @rule_attr is not a file descriptor as expected;
> > - * - EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
> > + * - %EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
> >    *   @rule_attr is not the expected file descriptor type;
> > - * - EPERM: @ruleset_fd has no write access to the underlying ruleset;
> > - * - EFAULT: @rule_attr inconsistency.
> > + * - %EPERM: @ruleset_fd has no write access to the underlying ruleset;
> > + * - %EFAULT: @rule_attr inconsistency.
> >    */
> >   SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
> >   		const enum landlock_rule_type, rule_type,
> > @@ -378,20 +378,20 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
> >    * @flags: Must be 0.
> >    *
> >    * This system call enables to enforce a Landlock ruleset on the current
> > - * thread.  Enforcing a ruleset requires that the task has CAP_SYS_ADMIN in its
> > + * thread.  Enforcing a ruleset requires that the task has %CAP_SYS_ADMIN in its
> >    * namespace or is running with no_new_privs.  This avoids scenarios where
> >    * unprivileged tasks can affect the behavior of privileged children.
> >    *
> >    * Possible returned errors are:
> >    *
> > - * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > - * - EINVAL: @flags is not 0.
> > - * - EBADF: @ruleset_fd is not a file descriptor for the current thread;
> > - * - EBADFD: @ruleset_fd is not a ruleset file descriptor;
> > - * - EPERM: @ruleset_fd has no read access to the underlying ruleset, or the
> > + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
> > + * - %EINVAL: @flags is not 0.
> > + * - %EBADF: @ruleset_fd is not a file descriptor for the current thread;
> > + * - %EBADFD: @ruleset_fd is not a ruleset file descriptor;
> > + * - %EPERM: @ruleset_fd has no read access to the underlying ruleset, or the
> >    *   current thread is not running with no_new_privs, or it doesn't have
> > - *   CAP_SYS_ADMIN in its namespace.
> > - * - E2BIG: The maximum number of stacked rulesets is reached for the current
> > + *   %CAP_SYS_ADMIN in its namespace.
> > + * - %E2BIG: The maximum number of stacked rulesets is reached for the current
> >    *   thread.
> >    */
> >   SYSCALL_DEFINE2(landlock_restrict_self, const int, ruleset_fd, const __u32,
> > --
> > 2.37.2