[PATCH v1 3/4] landlock_add_rule.2: Document new syscall

["Mickaël Salaün" <mic@digikod.net>]

From: Mickaël Salaün <mic@linux.microsoft.com>

This is an adaptation of
https://www.kernel.org/doc/html/v5.13/userspace-api/landlock.html

Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20210706182217.32338-4-mic@digikod.net
---
 man2/landlock_add_rule.2 | 139 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 man2/landlock_add_rule.2

diff --git a/man2/landlock_add_rule.2 b/man2/landlock_add_rule.2
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+.\" Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+.\" Copyright © 2019-2020 ANSSI
+.\" Copyright © 2021 Microsoft Corporation
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH LANDLOCK_ADD_RULE 2 2021-06-27 Linux "Linux Programmer's Manual"
+.SH NAME
+landlock_add_rule \- add a new Landlock rule to a ruleset
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/landlock.h>" "  /* Definition of " LANDLOCK_* " constants */"
+.BR "#include <sys/syscall.h>" "     /* Definition of " SYS_* " constants */"
+.PP
+.BI "int syscall(SYS_landlock_add_rule, int " ruleset_fd ,
+.BI "            enum landlock_rule_type " rule_type ,
+.BI "            const void * " rule_attr ", __u32 " flags );
+.SH DESCRIPTION
+A Landlock rule describes an action on an object.  An object is currently a
+file hierarchy, and the related filesystem actions are defined with a set
+of access rights.  This
+.BR landlock_add_rule (2)
+system call enables adding a new Landlock rule to an existing ruleset
+created with
+.BR landlock_create_ruleset (2)
+\&.  See
+.BR landlock (7)
+for a global overview.
+.PP
+.I ruleset_fd
+is a Landlock ruleset file descriptor obtained with
+.BR landlock_create_ruleset (2)
+\&.
+.PP
+.I rule_type
+identifies the structure type pointed to by
+.I rule_attr
+\&. Currently, Linux supports the following
+.I rule_type
+value:
+.TP
+.BR LANDLOCK_RULE_PATH_BENEATH
+This defines the object type as a file hierarchy.
+In this case,
+.I rule_attr
+points to the following structure:
+.IP
+.in +4n
+.EX
+struct landlock_path_beneath_attr {
+    __u64 allowed_access;
+    __s32 parent_fd;
+} __attribute__((packed));
+.EE
+.in
+.IP
+.I allowed_access
+contains a bitmask of allowed filesystem actions for this file hierarchy
+(see
+.BR "Filesystem actions"
+in
+.BR landlock (7)
+).
+.IP
+.I parent_fd
+is an opened file descriptor, preferably with the
+.I O_PATH
+flag, which identifies the parent directory of the file hierarchy or a just
+file.
+.PP
+.I flags
+must be 0.
+.SH RETURN VALUE
+On success,
+.BR landlock_add_rule (2)
+returns 0.
+.SH ERRORS
+.BR landlock_add_rule (2)
+can failed for the following reasons:
+.TP
+.BR EOPNOTSUPP
+Landlock is supported by the kernel but disabled at boot time.
+.TP
+.BR EINVAL
+.I flags
+is not 0, or the rule accesses are inconsistent (i.e.
+.I rule_attr->allowed_access
+is not a subset of the ruleset handled accesses).
+.TP
+.BR ENOMSG
+Empty accesses (i.e.
+.I rule_attr->allowed_access
+is 0).
+.TP
+.BR EBADF
+.I ruleset_fd
+is not a file descriptor for the current thread, or a member of
+.I rule_attr
+is not a file descriptor as expected.
+.TP
+.BR EBADFD
+.I ruleset_fd
+is not a ruleset file descriptor, or a member of
+.I rule_attr
+is not the expected file descriptor type.
+.TP
+.BR EPERM
+.I ruleset_fd
+has no write access to the underlying ruleset.
+.TP
+.BR EFAULT
+.I rule_attr
+was not a valid address.
+.SH VERSIONS
+Landlock was added in Linux 5.13.
+.SH SEE ALSO
+.BR landlock (7),
+.BR landlock_create_ruleset (2),
+.BR landlock_restrict_self (2)
-- 
2.32.0