[PATCH v4 0/4] Add Landlock man pages

[PATCH v4 0/4] Add Landlock man pages

[Mickaël Salaün]

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

Hi,

These four documents give a global overview of Landlock and explain each
system calls.  This is mainly a formatting of the current kernel
documentation with some new additional details.

This fourth patch series fixes spelling issues pointed out by Alejandro
Colomar and Branden Robinson.  I also removed some recipients.

This patch series can be found in a Git repository:
https://github.com/landlock-lsm/man-pages/commits/landlock-v4

Previous version:
https://lore.kernel.org/landlock/20210730144116.332091-1-mic@digikod.net/

Regards,

Mickaël Salaün (4):
  landlock.7: Add a new page to introduce Landlock
  landlock_create_ruleset.2: Document new syscall
  landlock_add_rule.2: Document new syscall
  landlock_restrict_self.2: Document new syscall

 man2/landlock_add_rule.2       | 144 +++++++++++++
 man2/landlock_create_ruleset.2 | 139 +++++++++++++
 man2/landlock_restrict_self.2  | 133 ++++++++++++
 man7/landlock.7                | 361 +++++++++++++++++++++++++++++++++
 4 files changed, 777 insertions(+)
 create mode 100644 man2/landlock_add_rule.2
 create mode 100644 man2/landlock_create_ruleset.2
 create mode 100644 man2/landlock_restrict_self.2
 create mode 100644 man7/landlock.7


base-commit: 7127973e0c8ca36fda1f5d2d0adae04d61fa0d01
-- 
2.32.0

[PATCH v4 1/4] landlock.7: Add a new page to introduce Landlock

[Mickaël Salaün]

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

From the user point of view, Landlock is a set of system calls enabling
to build and enforce a set of access-control rules.  A ruleset can be
created with landlock_create_ruleset(2), populated with
landlock_add_rule(2) and enforced with landlock_restrict_self(2).  This
man page gives an overview of the whole mechanism.  Details of these
system calls are documented in their respective man pages.

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/20210818155931.484070-2-mic@digikod.net
---

Changes since v3:
* Fix each…its/their as pointed out by Branden and Alejandro.

Changes since v2:
* Fix semantic newlines according to Alejandro Colomar.
* Fix minor grammar issues spotted by Alejandro.
* Fix .IR and .BR use as explained by Alejandro.

Changes since v1:
* Replace all ".I" with ".IR", except when used for titles.
* Append punctuation to ".IR" and ".BR" when it makes sense (requested
  by Alejandro Colomar).
* Cut lines according to the semantic newline rules (requested by
  Alejandro Colomar).
* Remove roman style from ".TP" section titles (requested by Alejandro
  Colomar).
* Add comma after "i.e." and "e.g.".
* Move the example in a new EXAMPLES section.
* Improve title.
* Explain the LSM acronym at first use.
---
 man7/landlock.7 | 361 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 361 insertions(+)
 create mode 100644 man7/landlock.7

diff --git a/man7/landlock.7 b/man7/landlock.7
new file mode 100644
index 000000000000..710e7feb7924
--- /dev/null
+++ b/man7/landlock.7
@@ -0,0 +1,361 @@
+.\" 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 7 2021-06-27 Linux "Linux Programmer's Manual"
+.SH NAME
+Landlock \- unprivileged access-control
+.SH DESCRIPTION
+Landlock is an access-control system that enables any processes to
+securely restrict themselves and their future children.
+Because Landlock is a stackable Linux Security Module (LSM),
+it makes it possible to create safe security sandboxes as new security
+layers in addition to the existing system-wide access-controls.
+This kind of sandbox is expected to help mitigate
+the security impact of bugs,
+and unexpected or malicious behaviors in applications.
+.PP
+A Landlock security policy is a set of access rights
+(e.g., open a file in read-only, make a directory, etc.)
+tied to a file hierarchy.
+Such policy can be configured and enforced by processes for themselves
+using three system calls:
+.IP \(bu 2
+.BR landlock_create_ruleset (2)
+creates a new ruleset;
+.IP \(bu
+.BR landlock_add_rule (2)
+adds a new rule to a ruleset;
+.IP \(bu
+.BR landlock_restrict_self (2)
+enforces a ruleset on the calling thread.
+.PP
+To be able to use these system calls,
+the running kernel must support Landlock and
+it must be enabled at boot time.
+.\"
+.SS Landlock rules
+A Landlock rule describes an action on an object.
+An object is currently a file hierarchy,
+and the related filesystem actions are defined with access rights (see
+.BR landlock_add_rule (2)).
+A set of rules is aggregated in a ruleset,
+which can then restrict the thread enforcing it,
+and its future children.
+.\"
+.SS Filesystem actions
+These flags enable to restrict a sandboxed process to a
+set of actions on files and directories.
+Files or directories opened before the sandboxing
+are not subject to these restrictions.
+See
+.BR landlock_add_rule (2)
+and
+.BR landlock_create_ruleset (2)
+for more context.
+.PP
+A file can only receive these access rights:
+.TP
+.B LANDLOCK_ACCESS_FS_EXECUTE
+Execute a file.
+.TP
+.B LANDLOCK_ACCESS_FS_WRITE_FILE
+Open a file with write access.
+.TP
+.B LANDLOCK_ACCESS_FS_READ_FILE
+Open a file with read access.
+.PP
+A directory can receive access rights related to files or directories.
+The following access right is applied to the directory itself,
+and the directories beneath it:
+.TP
+.B LANDLOCK_ACCESS_FS_READ_DIR
+Open a directory or list its content.
+.PP
+However,
+the following access rights only apply to the content of a directory,
+not the directory itself:
+.TP
+.B LANDLOCK_ACCESS_FS_REMOVE_DIR
+Remove an empty directory or rename one.
+.TP
+.B LANDLOCK_ACCESS_FS_REMOVE_FILE
+Unlink (or rename) a file.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_CHAR
+Create (or rename or link) a character device.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_DIR
+Create (or rename) a directory.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_REG
+Create (or rename or link) a regular file.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_SOCK
+Create (or rename or link) a UNIX domain socket.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_FIFO
+Create (or rename or link) a named pipe.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_BLOCK
+Create (or rename or link) a block device.
+.TP
+.B LANDLOCK_ACCESS_FS_MAKE_SYM
+Create (or rename or link) a symbolic link.
+.\"
+.SS Layers of file path access rights
+Each time a thread enforces a ruleset on itself,
+it updates its Landlock domain with a new layer of policy.
+Indeed, this complementary policy is composed with the potentially other
+rulesets already restricting this thread.
+A sandboxed thread can then safely add more constraints to itself with a
+new enforced ruleset.
+.PP
+One policy layer grants access to a file path
+if at least one of its rules encountered on the path grants the access.
+A sandboxed thread can only access a file path
+if all its enforced policy layers grant the access
+as well as all the other system access controls
+(e.g., filesystem DAC, other LSM policies, etc.).
+.\"
+.SS Bind mounts and OverlayFS
+Landlock enables restricting access to file hierarchies,
+which means that these access rights can be propagated with bind mounts
+(cf.
+.BR mount_namespaces (7))
+but not with OverlayFS.
+.PP
+A bind mount mirrors a source file hierarchy to a destination.
+The destination hierarchy is then composed of the exact same files,
+on which Landlock rules can be tied,
+either via the source or the destination path.
+These rules restrict access when they are encountered on a path,
+which means that they can restrict access to
+multiple file hierarchies at the same time,
+whether these hierarchies are the result of bind mounts or not.
+.PP
+An OverlayFS mount point consists of upper and lower layers.
+These layers are combined in a merge directory, result of the mount point.
+This merge hierarchy may include files from the upper and lower layers,
+but modifications performed on the merge hierarchy
+only reflect on the upper layer.
+From a Landlock policy point of view,
+each of the OverlayFS layers and merge hierarchies is standalone and
+contains its own set of files and directories,
+which is different from a bind mount.
+A policy restricting an OverlayFS layer will not restrict the resulted
+merged hierarchy, and vice versa.
+Landlock users should then only think about file hierarchies they want to
+allow access to, regardless of the underlying filesystem.
+.\"
+.SS Inheritance
+Every new thread resulting from a
+.BR clone (2)
+inherits Landlock domain restrictions from its parent.
+This is similar to the
+.BR seccomp (2)
+inheritance or any other LSM dealing with tasks'
+.BR credentials (7).
+For instance, one process's thread may apply Landlock rules to itself,
+but they will not be automatically applied to other sibling threads
+(unlike POSIX thread credential changes, cf.
+.BR nptl (7)).
+.PP
+When a thread sandboxes itself,
+we have the guarantee that the related security policy
+will stay enforced on all this thread's descendants.
+This allows creating standalone and modular security policies
+per application,
+which will automatically be composed between themselves
+according to their runtime parent policies.
+.\"
+.SS Ptrace restrictions
+A sandboxed process has less privileges than a non-sandboxed process and
+must then be subject to additional restrictions
+when manipulating another process.
+To be allowed to use
+.BR ptrace (2)
+and related syscalls on a target process,
+a sandboxed process should have a subset of the target process rules,
+which means the tracee must be in a sub-domain of the tracer.
+.SH VERSIONS
+Landlock was added in Linux 5.13.
+.SH NOTES
+Landlock is enabled by
+.BR CONFIG_SECURITY_LANDLOCK .
+The
+.I lsm=lsm1,...,lsmN
+command line parameter controls the sequence of the initialization of
+Linux Security Modules.
+It must contain the string
+.I landlock
+to enable Landlock.
+If the command line parameter is not specified,
+the initialization falls back to the value of the deprecated
+.I security=
+command line parameter and further to the value of CONFIG_LSM.
+We can check that Landlock is enabled by looking for
+.I landlock: Up and running.
+in kernel logs.
+.PP
+It is currently not possible to restrict some file-related actions
+accessible through these system call families:
+.BR chdir (2),
+.BR truncate (2),
+.BR stat (2),
+.BR flock (2),
+.BR chmod (2),
+.BR chown (2),
+.BR setxattr (2),
+.BR utime (2),
+.BR ioctl (2),
+.BR fcntl (2),
+.BR access (2).
+Future Landlock evolutions will enable to restrict them.
+.SH EXAMPLES
+We first need to create the ruleset that will contain our rules.
+For this example,
+the ruleset will contain rules that only allow read actions,
+but write actions will be denied.
+The ruleset then needs to handle both of these kind of actions.
+See below for the description of filesystem actions.
+.PP
+.in +4n
+.EX
+int ruleset_fd;
+struct landlock_ruleset_attr ruleset_attr = {
+    .handled_access_fs =
+        LANDLOCK_ACCESS_FS_EXECUTE |
+        LANDLOCK_ACCESS_FS_WRITE_FILE |
+        LANDLOCK_ACCESS_FS_READ_FILE |
+        LANDLOCK_ACCESS_FS_READ_DIR |
+        LANDLOCK_ACCESS_FS_REMOVE_DIR |
+        LANDLOCK_ACCESS_FS_REMOVE_FILE |
+        LANDLOCK_ACCESS_FS_MAKE_CHAR |
+        LANDLOCK_ACCESS_FS_MAKE_DIR |
+        LANDLOCK_ACCESS_FS_MAKE_REG |
+        LANDLOCK_ACCESS_FS_MAKE_SOCK |
+        LANDLOCK_ACCESS_FS_MAKE_FIFO |
+        LANDLOCK_ACCESS_FS_MAKE_BLOCK |
+        LANDLOCK_ACCESS_FS_MAKE_SYM,
+};
+
+ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+if (ruleset_fd < 0) {
+    perror("Failed to create a ruleset");
+    return 1;
+}
+.EE
+.in
+.PP
+We can now add a new rule to this ruleset thanks to the returned file
+descriptor referring to this ruleset.
+The rule will only allow reading the file hierarchy
+.IR /usr .
+Without another rule, write actions would then be denied by the ruleset.
+To add
+.I /usr
+to the ruleset, we open it with the
+.I O_PATH
+flag and fill the
+.I struct landlock_path_beneath_attr
+with this file descriptor.
+.PP
+.in +4n
+.EX
+int err;
+struct landlock_path_beneath_attr path_beneath = {
+    .allowed_access =
+        LANDLOCK_ACCESS_FS_EXECUTE |
+        LANDLOCK_ACCESS_FS_READ_FILE |
+        LANDLOCK_ACCESS_FS_READ_DIR,
+};
+
+path_beneath.parent_fd = open("/usr", O_PATH | O_CLOEXEC);
+if (path_beneath.parent_fd < 0) {
+    perror("Failed to open file");
+    close(ruleset_fd);
+    return 1;
+}
+err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+                        &path_beneath, 0);
+close(path_beneath.parent_fd);
+if (err) {
+    perror("Failed to update ruleset");
+    close(ruleset_fd);
+    return 1;
+}
+.EE
+.in
+.PP
+We now have a ruleset with one rule allowing read access to
+.I /usr
+while denying all other handled accesses for the filesystem.
+The next step is to restrict the current thread from gaining more
+privileges
+(e.g., thanks to a set-user-ID binary).
+.PP
+.in +4n
+.EX
+if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+    perror("Failed to restrict privileges");
+    close(ruleset_fd);
+    return 1;
+}
+.EE
+.in
+.PP
+The current thread is now ready to sandbox itself with the ruleset.
+.PP
+.in +4n
+.EX
+if (landlock_restrict_self(ruleset_fd, 0)) {
+    perror("Failed to enforce ruleset");
+    close(ruleset_fd);
+    return 1;
+}
+close(ruleset_fd);
+.EE
+.in
+.PP
+If the
+.BR landlock_restrict_self (2)
+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 ruleset.
+.PP
+Full working code can be found in
+.UR https://git.kernel.org\:/pub\:/scm\:/linux\:/kernel\:/git\:/stable\:/linux.git\:/tree\:/samples\:/landlock\:/sandboxer.c
+.UE
+.SH SEE ALSO
+.BR landlock_create_ruleset (2),
+.BR landlock_add_rule (2),
+.BR landlock_restrict_self (2)
+.PP
+.UR https://landlock.io\:/
+.UE
-- 
2.32.0

[PATCH v4 2/4] landlock_create_ruleset.2: Document new syscall

[Mickaël Salaün]

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/20210818155931.484070-3-mic@digikod.net
---

Changes since v2:
* Fix syscall signature (attr pointer).
* Add an EXAMPLES section referring to landlock(7).
* Change list order in the SEE ALSO section.
* Fix .IR and .BR use as explained by Alejandro Colomar.

Changes since v1:
* Replace all ".I" with ".IR", except when used for titles.
* Append punctuation to ".IR" and ".BR" when it makes sense (requested
  by Alejandro Colomar).
* Cut lines according to the semantic newline rules (requested by
  Alejandro Colomar).
* Remove roman style from ".TP" section titles (requested by Alejandro
  Colomar).
* Add comma after "i.e." and "e.g.".
* Add a "CONFORMING TO" section.
* Replace "(2)" with "()" for the described syscall name.
---
 man2/landlock_create_ruleset.2 | 139 +++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 man2/landlock_create_ruleset.2

diff --git a/man2/landlock_create_ruleset.2 b/man2/landlock_create_ruleset.2
new file mode 100644
index 000000000000..e1ca4bcf8c86
--- /dev/null
+++ b/man2/landlock_create_ruleset.2
@@ -0,0 +1,139 @@
+.\" 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_CREATE_RULESET 2 2021-06-27 Linux "Linux Programmer's Manual"
+.SH NAME
+landlock_create_ruleset \- create a new Landlock 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_create_ruleset,
+.BI "            const struct landlock_ruleset_attr *" attr ,
+.BI "            size_t " size " , __u32 " flags );
+.SH DESCRIPTION
+A Landlock ruleset identifies a set of rules (i.e., actions on objects).
+This
+.BR landlock_create_ruleset ()
+system call enables creating a new file descriptor identifying a ruleset.
+This file descriptor can then be used by
+.BR landlock_add_rule (2)
+and
+.BR landlock_restrict_self (2).
+See
+.BR landlock (7)
+for a global overview.
+.PP
+.I attr
+specifies the properties of the new ruleset.
+It points to the following structure:
+.IP
+.in +4n
+.EX
+struct landlock_ruleset_attr {
+	__u64 handled_access_fs;
+};
+.EE
+.in
+.IP
+.I handled_access_fs
+is a bitmask of actions that is handled by this ruleset and should then be
+forbidden if no rule explicitly allow them
+(see
+.B Filesystem actions
+in
+.BR landlock (7)).
+This enables simply restricting ambient rights
+(e.g., global filesystem access) and is needed for compatibility reasons.
+.PP
+.I size
+must be specified as
+.I sizeof(struct landlock_ruleset_attr)
+for compatibility reasons.
+.PP
+.I flags
+must be 0 if
+.I attr
+is used.
+Otherwise,
+.I flags
+can be set to:
+.TP
+.B LANDLOCK_CREATE_RULESET_VERSION
+If
+.I attr
+is NULL and
+.I size
+is 0, then the returned value is the highest supported Landlock ABI version
+(starting at 1).
+This version can be used for a best-effort security approach,
+which is encouraged when user space is not pinned to a specific kernel
+version.
+All features documented in these man pages are available with the version
+1.
+.SH RETURN VALUE
+On success,
+.BR landlock_create_ruleset ()
+returns a new Landlock ruleset file descriptor, or a Landlock ABI version
+according to
+.IR flags .
+.SH ERRORS
+.BR landlock_create_ruleset ()
+can failed for the following reasons:
+.TP
+.B EOPNOTSUPP
+Landlock is supported by the kernel but disabled at boot time.
+.TP
+.B EINVAL
+Unknown
+.IR flags ,
+or unknown access, or too small
+.IR size .
+.TP
+.B E2BIG
+.I size
+is too big.
+.TP
+.B EFAULT
+.I attr
+was not a valid address.
+.TP
+.B ENOMSG
+Empty accesses (i.e.,
+.I attr->handled_access_fs
+is 0).
+.SH VERSIONS
+Landlock was added in Linux 5.13.
+.SH CONFORMING TO
+This system call is Linux-specific.
+.SH EXAMPLES
+See
+.BR landlock (7).
+.SH SEE ALSO
+.BR landlock_add_rule (2),
+.BR landlock_restrict_self (2),
+.BR landlock (7)
-- 
2.32.0

[PATCH v4 3/4] landlock_add_rule.2: Document new syscall

[Mickaël Salaün]

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/20210818155931.484070-4-mic@digikod.net
---

Changes since v2:
* Fix syscall's rule_attr pointer.
* Add an EXAMPLES section referring to landlock(7).
* Change list order in the SEE ALSO section.
* Fix .IR and .BR use as explained by Alejandro Colomar.

Changes since v1:
* Replace all ".I" with ".IR", except when used for titles.
* Append punctuation to ".IR" and ".BR" when it makes sense (requested
  by Alejandro Colomar).
* Cut lines according to the semantic newline rules (requested by
  Alejandro Colomar).
* Remove roman style from ".TP" section titles (requested by Alejandro
  Colomar).
* Add comma after "i.e." and "e.g.".
* Add a "CONFORMING TO" section.
* Replace "(2)" with "()" for the described syscall name.
---
 man2/landlock_add_rule.2 | 144 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 man2/landlock_add_rule.2

diff --git a/man2/landlock_add_rule.2 b/man2/landlock_add_rule.2
new file mode 100644
index 000000000000..eafb8f8201b7
--- /dev/null
+++ b/man2/landlock_add_rule.2
@@ -0,0 +1,144 @@
+.\" 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 ()
+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
+.IR rule_attr .
+Currently, Linux supports the following
+.I rule_type
+value:
+.TP
+.B 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
+.B 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
+just a file.
+.PP
+.I flags
+must be 0.
+.SH RETURN VALUE
+On success,
+.BR landlock_add_rule ()
+returns 0.
+.SH ERRORS
+.BR landlock_add_rule ()
+can failed for the following reasons:
+.TP
+.B EOPNOTSUPP
+Landlock is supported by the kernel but disabled at boot time.
+.TP
+.B 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
+.B ENOMSG
+Empty accesses (i.e.,
+.I rule_attr->allowed_access
+is 0).
+.TP
+.B 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
+.B 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
+.B EPERM
+.I ruleset_fd
+has no write access to the underlying ruleset.
+.TP
+.B EFAULT
+.I rule_attr
+was not a valid address.
+.SH VERSIONS
+Landlock was added in Linux 5.13.
+.SH CONFORMING TO
+This system call is Linux-specific.
+.SH EXAMPLES
+See
+.BR landlock (7).
+.SH SEE ALSO
+.BR landlock_create_ruleset (2),
+.BR landlock_restrict_self (2),
+.BR landlock (7)
-- 
2.32.0

[PATCH v4 4/4] landlock_restrict_self.2: Document new syscall

[Mickaël Salaün]

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/20210818155931.484070-5-mic@digikod.net
---

Changes since v2:
* Add an EXAMPLES section referring to landlock(7).
* Change list order in the SEE ALSO section.
* Fix .IR and .BR use as explained by Alejandro Colomar.

Changes since v1:
* Replace all ".I" with ".IR", except when used for titles.
* Append punctuation to ".IR" and ".BR" when it makes sense (requested
  by Alejandro Colomar).
* Cut lines according to the semantic newline rules (requested by
  Alejandro Colomar).
* Remove roman style from ".TP" section titles (requested by Alejandro
  Colomar).
* Add comma after "i.e." and "e.g.".
* Add a "CONFORMING TO" section.
* Replace "(2)" with "()" for the described syscall name.
---
 man2/landlock_restrict_self.2 | 133 ++++++++++++++++++++++++++++++++++
 1 file changed, 133 insertions(+)
 create mode 100644 man2/landlock_restrict_self.2

diff --git a/man2/landlock_restrict_self.2 b/man2/landlock_restrict_self.2
new file mode 100644
index 000000000000..4b10997e2fb6
--- /dev/null
+++ b/man2/landlock_restrict_self.2
@@ -0,0 +1,133 @@
+.\" 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_RESTRICT_SELF 2 2021-06-27 Linux "Linux Programmer's Manual"
+.SH NAME
+landlock_restrict_self \- enforce a Landlock 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_restrict_self, int " ruleset_fd ,
+.BI "            __u32 " flags );
+.SH DESCRIPTION
+Once a Landlock ruleset is populated with the desired rules, the
+.BR landlock_restrict_self ()
+system call enables enforcing this ruleset on the calling thread.
+See
+.BR landlock (7)
+for a global overview.
+.PP
+A thread can be restricted with multiple rulesets that are then composed
+together to form the thread's Landlock domain.
+This can be seen as a stack of rulesets but it is implemented in a more
+efficient way.
+A domain can only be updated in such a way that the constraints of each
+past and future composed rulesets will restrict the thread and its future
+children for their entire life.
+It is then possible to gradually enforce tailored access control policies
+with multiple independant rulesets coming from different sources
+(e.g., init system configuration, user session policy,
+built-in application policy).
+However, most applications should only need one call to
+.BR landlock_restrict_self ()
+and they should avoid arbitrary numbers of such calls because of the
+composed rulesets limit.
+Instead, developers are encouraged to build a tailored ruleset thanks to
+multiple calls to
+.BR landlock_add_rule (2).
+.PP
+In order to enforce a ruleset, either the caller must have the
+.B CAP_SYS_ADMIN
+capability in its user namespace, or the thread must already have the
+.I no_new_privs
+bit set.
+As for
+.BR seccomp (2),
+this avoids scenarios where unprivileged processes can affect the behavior
+of privileged children (e.g., because of set-user-ID binaries).
+If that bit was not already set by an ancestor of this thread,
+the thread must make the following call:
+.IP
+.EX
+prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+.EE
+.PP
+.I ruleset_fd
+is a Landlock ruleset file descriptor obtained with
+.BR landlock_create_ruleset (2)
+and fully populated with a set of calls to
+.BR landlock_add_rule (2).
+.PP
+.I flags
+must be 0.
+.SH RETURN VALUE
+On success,
+.BR landlock_restrict_self ()
+returns 0.
+.SH ERRORS
+.BR landlock_restrict_self ()
+can failed for the following reasons:
+.TP
+.B EOPNOTSUPP
+Landlock is supported by the kernel but disabled at boot time.
+.TP
+.B EINVAL
+.I flags
+is not 0.
+.TP
+.B EBADF
+.I ruleset_fd
+is not a file descriptor for the current thread.
+.TP
+.B EBADFD
+.I ruleset_fd
+is not a ruleset file descriptor.
+.TP
+.B EPERM
+.I ruleset_fd
+has no read access to the underlying ruleset,
+or the calling thread is not running with
+.IR no_new_privs ,
+or it doesn't have the
+.B CAP_SYS_ADMIN
+in its user namespace.
+.TP
+.B E2BIG
+The maximum number of composed rulesets is reached for the calling thread.
+This limit is currently 64.
+.SH VERSIONS
+Landlock was added in Linux 5.13.
+.SH CONFORMING TO
+This system call is Linux-specific.
+.SH EXAMPLES
+See
+.BR landlock (7).
+.SH SEE ALSO
+.BR landlock_create_ruleset (2),
+.BR landlock_add_rule (2),
+.BR landlock (7)
-- 
2.32.0

Re: [PATCH v4 0/4] Add Landlock man pages

[Mickaël Salaün]

Alejandro, is there something more to do or is it OK for you?

On 18/08/2021 17:59, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@linux.microsoft.com>
> 
> Hi,
> 
> These four documents give a global overview of Landlock and explain each
> system calls.  This is mainly a formatting of the current kernel
> documentation with some new additional details.
> 
> This fourth patch series fixes spelling issues pointed out by Alejandro
> Colomar and Branden Robinson.  I also removed some recipients.
> 
> This patch series can be found in a Git repository:
> https://github.com/landlock-lsm/man-pages/commits/landlock-v4
> 
> Previous version:
> https://lore.kernel.org/landlock/20210730144116.332091-1-mic@digikod.net/
> 
> Regards,
> 
> Mickaël Salaün (4):
>   landlock.7: Add a new page to introduce Landlock
>   landlock_create_ruleset.2: Document new syscall
>   landlock_add_rule.2: Document new syscall
>   landlock_restrict_self.2: Document new syscall
> 
>  man2/landlock_add_rule.2       | 144 +++++++++++++
>  man2/landlock_create_ruleset.2 | 139 +++++++++++++
>  man2/landlock_restrict_self.2  | 133 ++++++++++++
>  man7/landlock.7                | 361 +++++++++++++++++++++++++++++++++
>  4 files changed, 777 insertions(+)
>  create mode 100644 man2/landlock_add_rule.2
>  create mode 100644 man2/landlock_create_ruleset.2
>  create mode 100644 man2/landlock_restrict_self.2
>  create mode 100644 man7/landlock.7
> 
> 
> base-commit: 7127973e0c8ca36fda1f5d2d0adae04d61fa0d01
> 

Re: [PATCH v4 0/4] Add Landlock man pages

[Alejandro Colomar (man-pages)]

Hi Mickaël,

On 11/3/21 13:07, Mickaël Salaün wrote:
> Alejandro, is there something more to do or is it OK for you?

I applied the patchset, plus a few minor fixes (see below).

Thanks!

Alex

> 
> On 18/08/2021 17:59, Mickaël Salaün wrote:
>> From: Mickaël Salaün <mic@linux.microsoft.com>
>>
>> Hi,
>>
>> These four documents give a global overview of Landlock and explain each
>> system calls.  This is mainly a formatting of the current kernel
>> documentation with some new additional details.
>>
>> This fourth patch series fixes spelling issues pointed out by Alejandro
>> Colomar and Branden Robinson.  I also removed some recipients.
>>
>> This patch series can be found in a Git repository:
>> https://github.com/landlock-lsm/man-pages/commits/landlock-v4
>>
>> Previous version:
>> https://lore.kernel.org/landlock/20210730144116.332091-1-mic@digikod.net/
>>
>> Regards,
>>
>> Mickaël Salaün (4):
>>    landlock.7: Add a new page to introduce Landlock
>>    landlock_create_ruleset.2: Document new syscall
>>    landlock_add_rule.2: Document new syscall
>>    landlock_restrict_self.2: Document new syscall
>>
>>   man2/landlock_add_rule.2       | 144 +++++++++++++
>>   man2/landlock_create_ruleset.2 | 139 +++++++++++++
>>   man2/landlock_restrict_self.2  | 133 ++++++++++++
>>   man7/landlock.7                | 361 +++++++++++++++++++++++++++++++++
>>   4 files changed, 777 insertions(+)
>>   create mode 100644 man2/landlock_add_rule.2
>>   create mode 100644 man2/landlock_create_ruleset.2
>>   create mode 100644 man2/landlock_restrict_self.2
>>   create mode 100644 man7/landlock.7
>>
>>
>> base-commit: 7127973e0c8ca36fda1f5d2d0adae04d61fa0d01
>>

---
     landlock_add_rule.2, landlock_create_ruleset.2, 
landlock_restrict_self.2, landlock.7: Minor tweaks to Mickaël's patches

     - exit(EXIT_FAILURE) instead of return 1, for consistency with the
       rest of the manual pages.
     - Use old declarations: variables defined at the top, separate
       from code.  Initialization other than zero doesn't belong there.
     - Don't break URIs in weird ways (a trailing slash on a new line
       would be weird).
     - Break URIs after the slash; not before.  Per Branden's advise.
     - Use uint32_t instead of __u32 in prototypes.
     - tfix
     - A few semantic newline improvements.
     - ffix

     Cc: Mickaël Salaün <mic@digikod.net>
     Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>

diff --git a/man2/landlock_add_rule.2 b/man2/landlock_add_rule.2
index eafb8f820..c3f6e84e0 100644
--- a/man2/landlock_add_rule.2
+++ b/man2/landlock_add_rule.2
@@ -34,10 +34,12 @@ landlock_add_rule \- add a new Landlock rule to a 
ruleset
  .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 );
+.BI "            const void *" rule_attr ", uint32_t " flags );
+.fi
  .SH DESCRIPTION
  A Landlock rule describes an action on an object.
-An object is currently a file hierarchy, and the related filesystem actions
+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 ()
@@ -114,13 +116,15 @@ is 0).
  .TP
  .B EBADF
  .I ruleset_fd
-is not a file descriptor for the current thread, or a member of
+is not a file descriptor for the current thread,
+or a member of
  .I rule_attr
  is not a file descriptor as expected.
  .TP
  .B EBADFD
  .I ruleset_fd
-is not a ruleset file descriptor, or a member of
+is not a ruleset file descriptor,
+or a member of
  .I rule_attr
  is not the expected file descriptor type.
  .TP
diff --git a/man2/landlock_create_ruleset.2 b/man2/landlock_create_ruleset.2
index e1ca4bcf8..11a8f08de 100644
--- a/man2/landlock_create_ruleset.2
+++ b/man2/landlock_create_ruleset.2
@@ -34,7 +34,8 @@ landlock_create_ruleset \- create a new Landlock ruleset
  .PP
  .BI "int syscall(SYS_landlock_create_ruleset,
  .BI "            const struct landlock_ruleset_attr *" attr ,
-.BI "            size_t " size " , __u32 " flags );
+.BI "            size_t " size " , uint32_t " flags );
+.fi
  .SH DESCRIPTION
  A Landlock ruleset identifies a set of rules (i.e., actions on objects).
  This
@@ -55,14 +56,14 @@ It points to the following structure:
  .in +4n
  .EX
  struct landlock_ruleset_attr {
-       __u64 handled_access_fs;
+    __u64 handled_access_fs;
  };
  .EE
  .in
  .IP
  .I handled_access_fs
-is a bitmask of actions that is handled by this ruleset and should then be
-forbidden if no rule explicitly allow them
+is a bitmask of actions that is handled by this ruleset and
+should then be forbidden if no rule explicitly allows them
  (see
  .B Filesystem actions
  in
@@ -98,12 +99,13 @@ All features documented in these man pages are 
available with the version
  .SH RETURN VALUE
  On success,
  .BR landlock_create_ruleset ()
-returns a new Landlock ruleset file descriptor, or a Landlock ABI version
+returns a new Landlock ruleset file descriptor,
+or a Landlock ABI version,
  according to
  .IR flags .
  .SH ERRORS
  .BR landlock_create_ruleset ()
-can failed for the following reasons:
+can fail for the following reasons:
  .TP
  .B EOPNOTSUPP
  Landlock is supported by the kernel but disabled at boot time.
diff --git a/man2/landlock_restrict_self.2 b/man2/landlock_restrict_self.2
index 4b10997e2..77c71bbf8 100644
--- a/man2/landlock_restrict_self.2
+++ b/man2/landlock_restrict_self.2
@@ -33,7 +33,7 @@ landlock_restrict_self \- enforce a Landlock ruleset
  .BR "#include <sys/syscall.h>" "     /* Definition of " SYS_* " 
constants */"
  .PP
  .BI "int syscall(SYS_landlock_restrict_self, int " ruleset_fd ,
-.BI "            __u32 " flags );
+.BI "            uint32_t " flags );
  .SH DESCRIPTION
  Once a Landlock ruleset is populated with the desired rules, the
  .BR landlock_restrict_self ()
@@ -42,13 +42,13 @@ See
  .BR landlock (7)
  for a global overview.
  .PP
-A thread can be restricted with multiple rulesets that are then composed
-together to form the thread's Landlock domain.
-This can be seen as a stack of rulesets but it is implemented in a more
-efficient way.
-A domain can only be updated in such a way that the constraints of each
-past and future composed rulesets will restrict the thread and its future
-children for their entire life.
+A thread can be restricted with multiple rulesets that are then
+composed together to form the thread's Landlock domain.
+This can be seen as a stack of rulesets but
+it is implemented in a more efficient way.
+A domain can only be updated in such a way that
+the constraints of each past and future composed rulesets
+will restrict the thread and its future children for their entire life.
  It is then possible to gradually enforce tailored access control policies
  with multiple independant rulesets coming from different sources
  (e.g., init system configuration, user session policy,
@@ -68,8 +68,8 @@ capability in its user namespace, or the thread must 
already have the
  bit set.
  As for
  .BR seccomp (2),
-this avoids scenarios where unprivileged processes can affect the behavior
-of privileged children (e.g., because of set-user-ID binaries).
+this avoids scenarios where unprivileged processes can affect
+the behavior of privileged children (e.g., because of set-user-ID 
binaries).
  If that bit was not already set by an ancestor of this thread,
  the thread must make the following call:
  .IP
@@ -91,7 +91,7 @@ On success,
  returns 0.
  .SH ERRORS
  .BR landlock_restrict_self ()
-can failed for the following reasons:
+can fail for the following reasons:
  .TP
  .B EOPNOTSUPP
  Landlock is supported by the kernel but disabled at boot time.
diff --git a/man7/landlock.7 b/man7/landlock.7
index 710e7feb7..80d9f2bf1 100644
--- a/man7/landlock.7
+++ b/man7/landlock.7
@@ -31,8 +31,9 @@ Landlock \- unprivileged access-control
  Landlock is an access-control system that enables any processes to
  securely restrict themselves and their future children.
  Because Landlock is a stackable Linux Security Module (LSM),
-it makes it possible to create safe security sandboxes as new security
-layers in addition to the existing system-wide access-controls.
+it makes it possible to create safe security sandboxes
+as new security layers in addition to
+the existing system-wide access-controls.
  This kind of sandbox is expected to help mitigate
  the security impact of bugs,
  and unexpected or malicious behaviors in applications.
@@ -128,8 +129,8 @@ Create (or rename or link) a symbolic link.
  .SS Layers of file path access rights
  Each time a thread enforces a ruleset on itself,
  it updates its Landlock domain with a new layer of policy.
-Indeed, this complementary policy is composed with the potentially other
-rulesets already restricting this thread.
+Indeed, this complementary policy is composed with the
+potentially other rulesets already restricting this thread.
  A sandboxed thread can then safely add more constraints to itself with a
  new enforced ruleset.
  .PP
@@ -165,8 +166,8 @@ From a Landlock policy point of view,
  each of the OverlayFS layers and merge hierarchies is standalone and
  contains its own set of files and directories,
  which is different from a bind mount.
-A policy restricting an OverlayFS layer will not restrict the resulted
-merged hierarchy, and vice versa.
+A policy restricting an OverlayFS layer will not restrict
+the resulted merged hierarchy, and vice versa.
  Landlock users should then only think about file hierarchies they want to
  allow access to, regardless of the underlying filesystem.
  .\"
@@ -244,9 +245,10 @@ See below for the description of filesystem actions.
  .PP
  .in +4n
  .EX
+struct landlock_ruleset_attr ruleset_attr = {0};
  int ruleset_fd;
-struct landlock_ruleset_attr ruleset_attr = {
-    .handled_access_fs =
+
+ruleset_attr.handled_access_fs =
          LANDLOCK_ACCESS_FS_EXECUTE |
          LANDLOCK_ACCESS_FS_WRITE_FILE |
          LANDLOCK_ACCESS_FS_READ_FILE |
@@ -259,13 +261,12 @@ struct landlock_ruleset_attr ruleset_attr = {
          LANDLOCK_ACCESS_FS_MAKE_SOCK |
          LANDLOCK_ACCESS_FS_MAKE_FIFO |
          LANDLOCK_ACCESS_FS_MAKE_BLOCK |
-        LANDLOCK_ACCESS_FS_MAKE_SYM,
-};
+        LANDLOCK_ACCESS_FS_MAKE_SYM;

  ruleset_fd = landlock_create_ruleset(&ruleset_attr, 
sizeof(ruleset_attr), 0);
-if (ruleset_fd < 0) {
+if (ruleset_fd == -1) {
      perror("Failed to create a ruleset");
-    return 1;
+    exit(EXIT_FAILURE);
  }
  .EE
  .in
@@ -285,19 +286,19 @@ with this file descriptor.
  .PP
  .in +4n
  .EX
+struct landlock_path_beneath_attr path_beneath = {0};
  int err;
-struct landlock_path_beneath_attr path_beneath = {
-    .allowed_access =
+
+path_beneath.allowed_access =
          LANDLOCK_ACCESS_FS_EXECUTE |
          LANDLOCK_ACCESS_FS_READ_FILE |
-        LANDLOCK_ACCESS_FS_READ_DIR,
-};
+        LANDLOCK_ACCESS_FS_READ_DIR;

  path_beneath.parent_fd = open("/usr", O_PATH | O_CLOEXEC);
-if (path_beneath.parent_fd < 0) {
+if (path_beneath.parent_fd == -1) {
      perror("Failed to open file");
      close(ruleset_fd);
-    return 1;
+    exit(EXIT_FAILURE);
  }
  err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
                          &path_beneath, 0);
@@ -305,7 +306,7 @@ close(path_beneath.parent_fd);
  if (err) {
      perror("Failed to update ruleset");
      close(ruleset_fd);
-    return 1;
+    exit(EXIT_FAILURE);
  }
  .EE
  .in
@@ -322,7 +323,7 @@ privileges
  if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
      perror("Failed to restrict privileges");
      close(ruleset_fd);
-    return 1;
+    exit(EXIT_FAILURE);
  }
  .EE
  .in
@@ -334,7 +335,7 @@ The current thread is now ready to sandbox itself 
with the ruleset.
  if (landlock_restrict_self(ruleset_fd, 0)) {
      perror("Failed to enforce ruleset");
      close(ruleset_fd);
-    return 1;
+    exit(EXIT_FAILURE);
  }
  close(ruleset_fd);
  .EE
@@ -342,20 +343,20 @@ close(ruleset_fd);
  .PP
  If the
  .BR landlock_restrict_self (2)
-system call succeeds, the current thread is now restricted and this policy
-will be enforced on all its subsequently created children as well.
+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 ruleset.
  .PP
  Full working code can be found in
-.UR 
https://git.kernel.org\:/pub\:/scm\:/linux\:/kernel\:/git\:/stable\:/linux.git\:/tree\:/samples\:/landlock\:/sandboxer.c
+.UR 
https://git.kernel.org/\:pub/\:scm/\:linux/\:kernel/\:git/\:stable/\:linux.git/\:tree/\:samples/\:landlock/\:sandboxer.c
  .UE
  .SH SEE ALSO
  .BR landlock_create_ruleset (2),
  .BR landlock_add_rule (2),
  .BR landlock_restrict_self (2)
  .PP
-.UR https://landlock.io\:/
+.UR https://landlock.io/
  .UE


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/