Message-ID: <CAHc6FU67LnV7-roofFe1y_uTfvgwonRZimyu7Wn1CDRzwHZJSw@mail.gmail.com>
Date:	Tue, 23 Feb 2016 16:09:02 +0100
From:	Andreas Gruenbacher <agruenba@...hat.com>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	linux-cifs@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Anna Schumaker <anna.schumaker@...app.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Andreas Dilger <adilger@...ger.ca>
Subject: Re: richacl(7) man page review comments

Hi Michael,

On Tue, Feb 23, 2016 at 11:58 AM, Michael Kerrisk (man-pages)
<mtk.manpages@...il.com> wrote:
> On 02/22/2016 03:46 PM, Andreas Gruenbacher wrote:
>> On Sun, Feb 21, 2016 at 10:40 PM, Michael Kerrisk (man-pages) <mtk.manpages@...il.com> wrote:
>>> I've once more pulled from the latest git; here's some more comments.
>>
>> thanks again. I've updated the repo with your changes.
>
> Next round :-). Just a few quick comments while I'm on a train ride.

applied, thanks.

>> .\"
>> .\" RichACL Manual Pages
>> .\"
>> .\" Copyright (C) 2015,2016  Red Hat, Inc.
>> .\" Written by Andreas Gruenbacher <agruenba@...hat.com>
>> .\" This is free documentation; you can redistribute it and/or
>> .\" modify it under the terms of the GNU General Public License as
>> .\" published by the Free Software Foundation; either version 2 of
>> .\" the License, or (at your option) any later version.
>> .\"
>> .\" The GNU General Public License's references to "object code"
>> .\" and "executables" are to be interpreted as the output of any
>> .\" document formatting or typesetting system, including
>> .\" intermediate and printed output.
>> .\"
>> .\" This manual is distributed in the hope that it will be useful,
>> .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
>> .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> .\" GNU General Public License for more details.
>> .\"
>> .\" You should have received a copy of the GNU General Public
>> .\" License along with this manual.  If not, see
>> .\" <http://www.gnu.org/licenses/>.
>> .\"
>> .de URL
>> \\$2 \(laURL: \\$1 \(ra\\$3
>> ..
>> .if \n[.g] .mso www.tmac
>> .TH RICHACL 7 2015-09-01 "Linux" "Rich Access Control Lists"
>> .SH NAME
>> richacl \- Rich Access Control Lists
>> .SH DESCRIPTION
>> Rich Access Control Lists (RichACLs) are an extension of the POSIX file
>> permission model (see
>> .BR acl (5))
>> to support
>> .URL https://tools.ietf.org/rfc/rfc5661.txt "NFSv4 Access Control Lists"
>> on local and remote-mounted filesystems.
>>
>> A RichACL can always be translated into an equivalent NFSv4 ACL which grants
>> the same permissions.
>>
>> RichACLs can be enabled on supported local filesystems (currently, ext4 and
>> XFS).  The in-kernel NFSv4 server and client also include RichACL support.
>>
>> Enabling RichACLs disables POSIX Access Control Lists; the two ACL models
>> cannot coexist on the same filesystem.
>>
>> When used on a filesystem that does not support RichACLs, the
>> .BR getrichacl (1)
>> and
>> .BR setrichacl (1)
>> utilities will operate on the file permission bits instead:
>> .BR getrichacl (1)
>> will display the file permission bits as a RichACL; when a RichACL
>> is set with
>> .BR setrichacl (1)
>> which can be represented exactly by the file permission bits,
>> .BR setrichacl (1)
>> will set the file permission bits instead.  An attempt to set a RichACL that
>> cannot be represented exactly by the file permission bits results in an error.
>>
>> .SS Structure of RichACLs
>>
>> RichACLs consist of a number of ACL entries, three file masks, and a set of
>> flags specifying attributes of the ACL as a whole (by contrast with the
>> per-ACL-entry flags described below).
>>
>> Each of the ACL entries allows or denies some permissions to a particular user,
>> group, or special identifier. An ACL entry consists of four fields:
>>
>> .IP \(bu 2
>> A tag which specifies the user, group, or special identifier the entry applies
>> to.  Special identifiers can be the file owner
>> .RB ( owner@ ),
>> the owning group
>> .RB ( group@ ),
>> or everyone
>> .RB ( everyone@ ).
>> .IP \(bu
>> A set of permissions the entry allows or denies.
>> .IP \(bu
>> A set of flags that indicate whether the user or group identifier is mapped or
>> unmapped, and whether the entry has been and can be inherited.
>> .IP \(bu
>> A type field indicating whether the entry allows or denies the permissions
>> specified in the second field.
>> .PP
>> The owner, group, and other file masks further control which permissions the
>> ACL grants, subject to the
>> .BR masked "\ (" m )
>> and
>> .BR write_through "\ (" w )
>> ACL flags: when the permissions of a file or directory are changed with
>> .BR chmod (2),
>> the file masks are set based on the new file mode, and the
>> .B masked
>> and
>> .B write_through
>> ACL flags are set. Likewise, when a new file or directory inherits an ACL from
>> its parent directory, the file masks are set to the intersection between the
>> permissions granted by the inherited ACL and the
>> .I mode
>> parameter as given to
>> .BR open "(2), " mkdir (2),
>> and similar, and the
>> .B masked
>> ACL flag is set. In both cases, the file masks limit the permissions that the
>> ACL will grant.
>>
>> The purpose of the file masks is to allow traditional POSIX applications which
>> are unaware of RichACLs to place limits on the permissions granted by the
>> RichACL without causing the ACL entries to be modified.  Without the file mask,
>> the only alternative would be for the kernel to directly modify the ACL
>> entries.  However, this latter approach could have a "hysteresis effect",
>> whereby a RichACL-unaware application that performs a transition from one file
>> mode to another file mode and then back to the original file mode could cause
>> destruction of the permission information in ACL entries.  When creating files
>> or directories, the
>> .I mode
>> parameter to
>> .BR open "(2), " mkdir (2),
>> and similar would cause the same effect.
>
> s/cause/have/
>
>>
>> Note that entries with the identifier
>> .B everyone@
>> apply to all processes, whereas the \(lqother\(rq file permissions and
>> \(lqother\(rq entries in POSIX ACLs apply to all processes which are not the
>
> So, I still think it's helpful to mention ACL_OTHER here. How about:
>
> s/\\(lqother\\(rq/\\(lqother\\(rq (\\fBACL_OTHER\\fP)/
>
>> owner, are not in the owning group, and do not match a user or group mentioned
>> in the ACL.
>>
>> Unlike POSIX ACLs, RichACLs do not have separate \(lqaccess\(rq ACLs that
>> define the access permissions and \(lqdefault\(rq ACLs that define the
>> inheritable permissions.  Instead, flags on each ACL entry determine whether
>> the entry is effective during access checks and/or inheritable.
>>
>>
>> .SS ACL flags
>>
>> The following ACL flags are defined:
>>
>> .TP
>> .BR masked "\ (" m )
>> When set, the file masks define upper limits on the permissions the ACL may
>> grant.  When not set, the file masks are ignored.
>> .TP
>> .BR write_through "\ (" w )
>> When this flag and the
>> .B masked
>> flag are both set, the owner and other file masks define the actual permissions
>> granted to the file owner and to others instead of defining an upper limit.
>> When the
>> .B masked
>> flag is not set, the
>> .B write_through
>> flag has no effect.
>> .TP
>> .BR auto_inherit "\ (" a )
>> Automatic Inheritance is enabled.  See
>> .IR "Automatic Inheritance" .
>> .TP
>> .BR protected "\ (" p )
>> The ACL is protected from modification by Automatic
>> Inheritance.
>> .TP
>> .BR defaulted "\ (" d )
>> Indicates that the ACL has been assigned in an application-dependent way when
>> the file or directory was created; it has neither been inherited nor set
>> explicitly. ACLs of files created on Linux will never have the
>> .B defaulted
>> flag set, but the flag may be set on files created on or copied over from
>> other operating systems.  When this flag is set for an ACL, Automatic
>> Inheritance will completely replace the ACL.
>>
>> .SS ACL entry flags
>>
>> The following flags on ACL entries are defined:
>>
>> .TP
>> .BR file_inherit "\ (" f )
>> When this flag appears in the ACL entry of a directory, then:
>> .RS
>> .IP \(bu 2
>> That entry is inherited by new files created in the directory such that the
>> permissions of the entry apply to the file (the inheritance flags of the
>> inherited entry are cleared).
>> .IP \(bu
>> The entry is is inherited by new subdirectories created in the directory such
>> that the permissions of the entry will apply to new files created in the
>> subdirectory.
>> .RE
>> .TP
>> .BR dir_inherit "\ (" d )
>> When this flag appears in the ACL entry of a directory, then that entry is
>> inherited by new subdirectories created in the directory such that the
>> permissions of the entry apply to the subdirectory (the
>> .B inherit_only
>> flag is cleared).
>> .TP
>> .BR no_propagate "\ (" n )
>> Inheritance stops at the next subdirectory level.  When a file or directory
>> inherits an entry that has this flag set, the
>> .BR file_inherit ", " dir_inherit ", " no_propagate ", and " inherit_only
>> flags are cleared.
>> .TP
>> .BR inherit_only "\ (" i )
>> The entry defines inheritable permissions only and is ignored for access
>> checking.  When a file or directory inherits an entry that has this flag set,
>> the flag is cleared.
>> .TP
>> .BR inherited "\ (" a )
>> The entry has been automatically inherited from the parent directory.
>> .TP
>> .BR unmapped "\ (" u )
>> The user or group identifier is a textual string and is not mapped to a numeric
>> user or group identifier.  ACLs with unmapped identifiers can occur on NFSv4
>> mounted filesystems when the client cannot determine numeric user or group
>> identifiers for some of the NFSv4 user@...ain or group@...ain who values.  They
>> cannot be assigned to local files or directories.
>>
>> .SS Permissions
>>
>> The following permissions are defined for RichACL entries and for the three
>> file masks:
>>
>> .TP
>> .BR read_data " / " list_directory "\ (" r )
>> For a file: read the data of the file.
>> For a directory: list the contents of the directory.
>> .TP
>> .BR write_data " / " add_file "\ (" w )
>> For a file: modify the data of the file; does not include opening the file in
>> append mode.
>> For a directory: add a new file in the directory.
>> .TP
>> .BR append_data " / " add_subdirectory "\ (" p )
>> For a file: open the file in append mode.
>> For a directory: create a subdirectory in the directory.
>> .TP
>> .BR execute "\ (" x )
>> For a file: execute the file.
>> For a directory: traverse (search) the directory.
>> .TP
>> .BR delete_child "\ (" d )
>> Delete a file or directory within a directory.  This permission is meaningful
>> only for directories.
>> .TP
>> .BR delete "\ (" D )
>> Delete the file or directory.
>> .TP
>> .BR read_attributes "\ (" a )
>> Read basic attributes of a file or directory (see
>> .BR stat (2)).
>> This permission is defined by NFSv4.  It is stored, but ignored.  Reading basic
>> attributes of files and directories is always allowed on Linux.
>> .TP
>> .BR write_attributes "\ (" A )
>> Change the times associated with a file or directory to an arbitrary value.
>> This permission is always implicitly granted to the file owner.
>> .TP
>> .BR read_acl "\ (" c )
>> Read the ACL of a file or directory. Like reading the basic file attributes (the
>> .B read_attributes
>> permission), reading ACLs is always allowed in Linux.
>> .TP
>> .BR write_acl "\ (" C )
>> Change the ACL or file mode of a file or directory.
>> .TP
>> .BR write_owner "\ (" o )
>> Take ownership of a file or directory.  Change the owning group of a file or
>> directory to a group of which the calling process is a member.
>> .TP
>> .ad l
>> .BR read_named_attrs "\ (" R "), " write_named_attrs "\ (" W "), " synchronize "\ (" S "), " write_retention "\ (" e "), " write_retention_hold "\ (" E )
>> .ad
>> These permissions are defined by NFSv4 and NFSv4.1.  They are stored, but ignored.
>> .PP
>> For the
>> .BR r ", " w ", and " p
>> permissions, which have different long forms for files and directories, the
>> .BR getrichacl (1)
>> utility will output the appropriate form(s) depending on the context.
>> The
>> .BR setrichacl (1)
>> utility will accept either form for any file type.
>>
>> .SS Text form
>> The common textual representation of a RichACL consists of the colon-separated
>> fields of the ACL flags, file masks, and ACL entries in the following
>> format:
>> .TP
>> \fBflags:\fR\fIacl_flags\fR
>> The ACL flags.
>> .TP
>> \fBowner:\fR\fIperm\fR\fB::mask\fR, \fBgroup:\fR\fIperm\fR\fB::mask\fR, \fBother:\fR\fIperm\fR\fB::mask\fR
>> The file masks and their permissions.
>> .TP
>> \fIwho\fR\fB:\fR\fIperm\fR\fB:\fR\fIflags\fR\fB:allow\fR, \fIwho\fR\fB:\fR\fIperm\fR\fB:\fR\fIflags\fR\fB:deny\fR
>> For each ACL entry, who the entry applies to, the permissions of the entry, the
>> entry flags, and the entry type. The \fIwho\fR field is one of the following:
>> .RS
>> .IP \(bu 2
>> One of the special identifiers:
>> .BR owner@ ", " group@ ", or " everyone@ ,
>> .IP \(bu
>> A
>> .BR user: " or " u:
>> prefix followed by a user name or user ID that designates a specific user,
>> .IP \(bu
>> A
>> .BR group: " or " g:
>> prefix followed by a group name or group ID that designates a specific group.
>> .RE
>> .PP
>> The entries are comma, whitespace, or newline separated.
>
> s/entries/fields of an ACL entry/ (?)

No, the fields in each of the different kinds of entries are colon separated.

"The ACL flags, file masks, and ACL entries are comma, whitespace, or newline
separated."

>> Flags and permissions have single-letter as well as long forms, as listed under
>> .IR "ACL flags" ,
>> .IR "ACL entry flags" ,
>> and
>> .IR Permissions .
>> When the single-letter forms are used, the flags or permissions are
>> concatenated. When the long forms are used, the flags or permissions are
>> separated by slashes.  To align permissions or flags vertically, dashes can be
>> used for padding.
>>
>> .SS Setting and modifying file permissions
>> The access permissions for a file can either be set by assigning an Access
>> Control List
>> .RB ( setrichacl (1))
>> or by changing the file mode permission bits
>> .RB ( chmod (1)).
>> In addition, a file can inherit an ACL from its parent directory at creation
>> time as described under
>> .IR "Permissions at file-creation time" .
>>
>> .SS Assigning an Access Control List
>> When assigning an ACL to a file, unless explicitly specified, the owner, group,
>> and other file masks will be computed from the ACL entries as described in
>> the section
>> .IR "Computing the maximum file masks" .
>> The owner, group, and other file mode permission bits are then each set from
>> the owner, group, and other file mask as follows:
>> .IP \(bu 2
>> If the file mask includes the
>> .B r
>> permission, the read
>> file mode permission bit will be set.
>> .IP \(bu
>> If the file mask includes the
>> .B w
>> or
>> .B p
>> permission, the write file mode permission bit will be set.
>> .IP \(bu
>> If the file mask includes the
>> .B x
>> permission, the execute file mode permission bit will be set.
>> .PP
>> If the ACL can be represented exactly by the file mode permission bits, the
>> file permission bits are set to match the ACL and no ACL is stored.  (When the
>> ACL of a file is requested which doesn't have an ACL, the file mode permission
>> bits are converted into an equivalent ACL.)
>>
>> .SS Changing the file mode permission bits
>> When changing the file mode permission bits with
>> .BR chmod (1),
>> the owner, group, and other file permission bits are set to the permission bits
>> in the new mode, and the owner, group, and other file masks are set based on
>> the new mode bits as follows:
>> .IP \(bu 2
>> If the read bit in a set of permissions is set, the
>> .B r
>> permission in the corresponding file mask will be set.
>> .IP \(bu
>> If the write bit in a set of permissions is set, the
>> .B w
>> and
>> .B p
>> permissions in the corresponding file mask will be set.
>> .IP \(bu
>> If the execute bit in a set of permissions is set, the
>> .B x
>> permission in the corresponding file mask will be set.
>> .PP
>> In addition, the
>> .B masked
>> and
>> .B write_through
>> ACL flags are set. This has the
>> effect of limiting the permissions granted by the ACL to the file mode
>> permission bits; in addition, the owner is granted the owner mode bits and
>> others are granted the other mode bits. If the
>> .B auto_inherit
>> flag is set, the
>> .B protected
>> flag is also set to prevent the Automatic Inheritance algorithm from modifying
>> the ACL.
>>
>> .SS Permissions at file-creation time
>> When a directory has any inheritable ACL entries, the following
>> happens when a file or directory is created inside that directory:
>> .RS 4
>
> Remove preceding line.
>
>> .IP 1. 4
>> A file created inside that directory will inherit all of the ACL entries that
>> have the
>> .B file_inherit
>> flag set, and all inheritance-related flags in the inherited entries flag will
>> be cleared.
>>
>> A subdirectory created inside that directory will inherit all of the ACL
>> entries that either have the
>> .B dir_inherit
>> flag set, or the
>> .B file_inherit
>> flag set and the
>> .B no_propagate
>> flag not set.  Entries whose
>> .B dir_inherit
>> flag is set will have their
>> .B inherit_only
>> flag cleared, and entries whose
>> .B dir_inherit
>> flag is not set will have their
>> .B inherit_only
>> flag set.  Finally, entries whose
>> .B no_propagate
>> flag is set will have all inheritance-related flags cleared.
>> .IP 2.
>> If the parent directory's ACL has the
>> .B auto_inherit
>> flag set, the inherited ACL will have its
>
> s/the/then the/
> (For ease of parsing)
>
>> .B auto_inherit
>> flag set, and all entries will have their
>> .B inherited
>> flag set.  Otherwise, the
>> .B auto_inherit
>> and
>> .B inherited
>> flags are cleared.
>> .IP 3.
>> The three file masks are computed from the inherited ACL as described in
>> the section
>> .IR "Computing the maximum file masks" .
>> .IP 4.
>> The three sets of permissions for the owner, the group, and for others in
>> the \fImode\fR parameter as given to
>> .BR open (2),
>> .BR mkdir (2),
>> and similar are converted into sets of RichACL permissions. The correspondence
>> between mask flags and RichACL permission bits is described in the section
>> .IR "Changing the file mode permission bits" .
>> Any RichACL permissions not included in those sets are
>> removed from the owner, group, and other file masks. The file mode permission
>> bits are then computed from the file masks as described in the section
>> .IR "Assigning an Access Control List" .
>> The process umask (see
>> .BR umask (2))
>> is ignored.
>> .IP 5.
>> The
>> .B masked
>> ACL flag is set. The
>> .B write_through
>> ACL flag remains cleared. In addition, if the
>> .B auto_inherit
>> flag of the inherited ACL is set, the
>> .B protected
>> flag is also set to prevent the Automatic Inheritance algorithm from modifying
>> the ACL.
>> .RE
>
> Remove preceding line.
>
>> .PP
>> When a directory does not have inheritable ACL entries, files and directories
>> created inside that directory will not be assigned Access Control Lists and the
>> file mode permission bits will be set to (\fImode\fR\ &\ ~\fIumask\fR) where
>> \fImode\fR is the mode argument of the relevant system call and \fIumask\fR is
>> the process umask (see
>> .BR umask (2)).
>>
>> .SS Automatic Inheritance
>> Automatic Inheritance is a mechanism that allows permission changes to
>> propagate from a directory to files and subdirectories inside that directory,
>> recursively.  Propagation is carried out by the process changing the directory
>> permissions (usually,
>> .BR setrichacl (1));
>> it happens without user intervention albeit not entirely automatically.
>>
>> A significant limitation is that this mechanism works only as long as files
>
> s/limitation/limitation of the Automatic Inheritance feature/
>
>> are created without explicitly specifying the file permissions to use. The
>> standard system calls for creating files and directories
>> .RB ( creat (2),
>> .BR open (2),
>> .BR mkdir (2),
>> .BR mknod (2))
>
> s/)$/,\nand so on)/
>
> (And, I'd drop creat(2) from that list of examples. It's ancient and
> obsolete; no need to encourageits use.)
>
>> all have mandatory mode parameters which define the maximum allowed permissions
>> of the new files. To take account of this restriction, the
>> .B protected
>> ACL flag must be set if the
>> .B inherited
>> flag is set. This effectively disables Automatic Inheritance for that
>> particular file.
>>
>> Notwithstanding the aforementioned limitation, Automatic Inheritance still
>> remains useful for network protocols like NFSv4 and SMB, which both support
>> creating files and directories without defining their permissions. These
>> protocols can implement those operations by using the standard system calls and
>> by then undoing the effect of applying the mode parameters.
>>
>> When the ACL of a directory is changed, the following happens for each entry
>> (\(lqchild\(rq) inside that directory:
>> .IP 1. 4
>> If the entry is a symbolic link, skip the child.
>> .IP 2.
>> If the
>> .B auto_inherit
>> flag of the entry's ACL is not set or the
>> .B protected
>> flag is set, skip the child.
>> .IP 3.
>> With the child's ACL:
>> .RS 4
>> .IP a) 4
>> If the
>> .B defaulted
>> flag is set, replace the ACL with an empty ACL
>> with the
>> .B auto_inherit
>> flag set.
>> .IP b)
>> Delete all entries which have the
>> .B inherited
>> flag set.
>> .IP c)
>> Append all entries inherited from the parent directory according to step 1 of
>> the algorithm described under
>> .IR "Permissions at file-creation time".
>> Set the
>> .B inherited
>> flag of each of these entries.
>> .IP d)
>> Recompute the file masks.
>
> At th end of the last section, add:
>
>         as descibed in the section "...."
>
>> .RE
>> .IP 4.
>> If the child is a directory, recursively apply this algorithm.
>>
>> .SS Access check algorithm
>>
>> When a process requests a particular kind of access (expressed as a set of
>> RichACL permissions) to a file, the following algorithm determines whether the
>> access is granted or denied:
>>
>> .IP 1. 4
>> If the
>> .B masked
>> ACL flag is set, then:
>> .RS 4
>> .IP a) 4
>> If the
>> .B write_through
>> ACL flag is set, then:
>> .RS 4
>> .IP \(bu 2
>> If the requesting process is the file owner, then access is granted if the
>> owner mask includes the requested permissions, and is otherwise denied.
>> .IP \(bu
>> If the requesting process is not the file owner and it is in the owning group or matches any ACL entries other than
>> .BR everyone@ ,
>> proceed to step b).
>> .IP \(bu
>> If the requesting process is not the file owner, is not in the owning group,
>> and no ACL entries other than
>> .B everyone@
>> match the process, then access is granted if the other mask includes the
>> requested permissions, and is otherwise denied.
>> .RE
>> .IP b)
>> If any of the following is true:
>> .RS 4
>> .IP \(bu 2
>> the requesting process is the file owner and the owner mask does not include all
>> requested permissions,
>> .IP \(bu
>> the requesting process is not the file owner and it is in the owning group or
>> matches any ACL entries other than
>> .BR everyone@ ,
>> and the group mask does not include all requested permissions,
>> .IP \(bu
>> the requesting process is not the file owner, not in the owning group, it
>> matches no ACL entries other than
>> .BR everyone@ ,
>> and the other mask does not include all requested permissions,
>> .PP
>> then access is denied.
>> .RE
>> .RE
>> .IP 2.
>> Upon reaching this point, the determination of whether or not access is granted
>> is made by scanning all ACL entries to see if one or more applicable entries
>> together grant a cumulative set of permissions that matches the requested
>> permissions or there is an applicable entry that explicitly denies one or more
>> of the requested permissions.  The scan of all ACL entries begins by first
>> initializing the set of remaining permissions (i.e., those that have not yet
>> been satisfied during the scan) to be the set of requested permissions. Then
>> the ACL entries are scanned
>> .IR "in order" ,
>> and for each entry:
>> .RS 4
>> .IP a) 4
>> If the
>> .B inherit_only
>> or
>> .B unmapped
>> flags are set, continue with the next ACL entry.
>> .IP b)
>> If any of the following is true:
>> .RS 4
>> .IP \(bu 2
>> the entry's identifier is
>> .B owner@
>> and the requesting process is the file owner,
>> .IP \(bu
>> the entry's identifier is
>> .B group@
>> and the requesting process is in the owning group,
>> .IP \(bu
>> the entry's identifier is a user and the requesting process is owned by that
>> user,
>> .IP \(bu
>> the entry's identifier is a group and the requesting process is a member in
>> that group,
>> .IP \(bu
>> the entry's identifier is
>> .BR everyone@ ,
>> .PP
>> then the entry matches the process; proceed to the next step. Otherwise,
>> continue with the next ACL entry.
>> .RE
>> .IP c)
>> If the entry denies any of the remaining permissions, access is denied.
>> .IP d)
>> If the entry allows any of the remaining permissions, then:
>> .RS 4
>> .IP \(bu 2
>> If the
>> .B masked
>> ACL flag is set and the entry's identifier is not
>> .B owner@
>> or
>> .BR everyone@
>> or is a user entry matching the file owner, remove all permissions from the
>> remaining permissions which are both allowed by the entry and included in the
>> group mask,
>> .IP \(bu
>> Otherwise, remove all permissions from the remaining permissions which are
>> allowed by the entry.
>> .RE
>> .RE
>> .IP 3.
>> If there are no more remaining permissions, access is allowed. Otherwise,
>> access is denied.
>> .PP
>> In this algorithm, a process can gain the permissions it requires by
>> accumulating them from multiple RichACL entries.  This is in contrast with
>> POSIX ACLs, where access is only granted if an ACL entry exists that matches
>> the requesting process and includes all the requested permissions.
>>
>> .SS Computing the maximum file masks
>> When setting an ACL and no file masks have been explicitly specified and when
>> inheriting an ACL from the parent directory, the following algorithm is used
>
> s/directory/directory (as described in section "....")/

Presumably "in the section" here as well.

>> for computing the file masks:
>>
>> .IP 1. 4
>> Clear the owner, group, and other file masks. Remember which permissions have
>> already been processed (initially, the empty set).
>> .IP 2.
>> For each ACL entry:
>> .RS 4
>> .IP \(bu 2
>> If the
>> .B inherit_only
>> flag is set, skip the entry.
>> .IP \(bu
>> Otherwise, compute which permissions the entry allows or denies that have not
>> been processed yet (the remaining permissions).
>> .IP \(bu
>> If the entry is an
>> .B owner@
>> entry, add the remaining permissions to the owner mask for
>> .B allow
>> entries, and remove the remaining permissions from the owner mask for
>> .B deny
>> entries.
>> .IP \(bu
>> Otherwise, if the entry is an
>> .B everyone@
>> entry, proceed as with
>> .B owner@
>> entries but add or remove the remaining permissions from the owner, group, and
>> other file masks.
>> .IP \(bu
>> Otherwise, proceed as with
>> .B owner@
>> entries but add or remove the remaining permissions from the owner and group
>> file masks.
>> .IP \(bu
>> Add the entry's permissions to the processed permissions.
>> .RE
>> .PP
>> The resulting file masks represent the ACL as closely as possible. With these
>> file masks, the effective permissions that the ACL grants will be the same when
>> the
>> .B masked
>> flag is set as when it is not set.
>>
>> .\" .SH BUGS
>> .SH AUTHOR
>> Written by Andreas Grünbacher <agruenba@...hat.com>.
>>
>> Please send your bug reports, suggested features and comments to the above address.
>>
>> .SH CONFORMING TO
>> Rich Access Control Lists are Linux-specific.
>> .SH SEE ALSO
>> .BR chmod (1),
>> .BR getrichacl (1),
>> .BR ls (1),
>> .BR setrichacl (1)
>> .BR stat (2),
>> .BR umask (2),
>> .BR acl (5)
>> .\" librichacl
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