[PATCH v3 1/2] landlock.7, landlock_*.2: Document Landlock ABI version 4

["Günther Noack" <gnoack@google.com>]

Landlock ABI 4 restricts bind(2) and connect(2) on TCP port numbers.

The intent is to bring the man pages mostly in line with the kernel
documentation again.  I intentionally did not add networking support to the
usage example in landlock.7 - I feel that in the long run, we would be better
advised to maintain longer example code in the kernel samples.

Closes: <https://github.com/landlock-lsm/linux/issues/32>
Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Reviewed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Günther Noack <gnoack@google.com>
---
 man/man2/landlock_add_rule.2       | 74 ++++++++++++++++++++++++++----
 man/man2/landlock_create_ruleset.2 | 12 ++++-
 man/man7/landlock.7                | 23 ++++++++--
 3 files changed, 94 insertions(+), 15 deletions(-)

diff --git a/man/man2/landlock_add_rule.2 b/man/man2/landlock_add_rule.2
index 7a83bb303..489e9c354 100644
--- a/man/man2/landlock_add_rule.2
+++ b/man/man2/landlock_add_rule.2
@@ -20,15 +20,14 @@ Standard C library
 .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
-are defined with a set of access rights.
-This
+A Landlock rule describes an action on an object
+which the process intends to perform.
+A set of rules is aggregated in a ruleset,
+which can then restrict the thread enforcing it, and its future children.
+.P
+The
 .BR landlock_add_rule ()
-system call enables adding a new Landlock rule to an existing ruleset
-created with
-.BR landlock_create_ruleset (2).
+system call adds a new Landlock rule to an existing ruleset.
 See
 .BR landlock (7)
 for a global overview.
@@ -42,10 +41,15 @@ identifies the structure type pointed to by
 .IR rule_attr .
 Currently, Linux supports the following
 .I rule_type
-value:
+values:
 .TP
 .B LANDLOCK_RULE_PATH_BENEATH
-This defines the object type as a file hierarchy.
+For these rules,
+the object is a file hierarchy,
+and the related filesystem actions
+are defined with
+.IR "filesystem access rights" .
+.IP
 In this case,
 .I rule_attr
 points to the following structure:
@@ -74,6 +78,45 @@ is an opened file descriptor, preferably with the
 flag,
 which identifies the parent directory of the file hierarchy or
 just a file.
+.TP
+.B LANDLOCK_RULE_NET_PORT
+For these rules,
+the object is a TCP port,
+and the related actions are defined with
+.IR "network access rights" .
+.IP
+In this case,
+.I rule_attr
+points to the following structure:
+.IP
+.in +4n
+.EX
+struct landlock_net_port_attr {
+    __u64 allowed_access;
+    __u64 port;
+};
+.EE
+.in
+.IP
+.i allowed_access
+contains a bitmask of allowed network actions,
+which can be applied on the given port.
+.IP
+.i port
+is the network port in host endianness.
+.IP
+It should be noted that port 0 passed to
+.BR bind (2)
+will bind to an available port from the ephemeral port range.
+This can be configured in the
+.I /proc/sys/net/ipv4/ip_local_port_range
+sysctl (also used for IPv6).
+.IP
+A Landlock rule with port 0
+and the
+.B LANDLOCK_ACCESS_NET_BIND_TCP
+right means that requesting to bind on port 0 is allowed
+and it will automatically translate to binding on the related port range.
 .P
 .I flags
 must be 0.
@@ -89,6 +132,12 @@ is set to indicate the error.
 .BR landlock_add_rule ()
 can fail for the following reasons:
 .TP
+.B EAFNOSUPPORT
+.I rule_type
+is
+.BR LANDLOCK_RULE_NET_PORT ,
+but TCP is not supported by the running kernel.
+.TP
 .B EOPNOTSUPP
 Landlock is supported by the kernel but disabled at boot time.
 .TP
@@ -111,6 +160,11 @@ are only applicable to directories, but
 .I \%rule_attr\->parent_fd
 does not refer to a directory).
 .TP
+.B EINVAL
+In
+.IR \%struct\~landlock_net_port_attr ,
+the port number is greater than 65535.
+.TP
 .B ENOMSG
 Empty accesses (i.e.,
 .I rule_attr\->allowed_access
diff --git a/man/man2/landlock_create_ruleset.2 b/man/man2/landlock_create_ruleset.2
index 105e9b062..ca635ddbc 100644
--- a/man/man2/landlock_create_ruleset.2
+++ b/man/man2/landlock_create_ruleset.2
@@ -41,6 +41,7 @@ It points to the following structure:
 .EX
 struct landlock_ruleset_attr {
     __u64 handled_access_fs;
+    __u64 handled_access_net;
 };
 .EE
 .in
@@ -52,6 +53,13 @@ is a bitmask of handled filesystem actions
 in
 .BR landlock (7)).
 .IP
+.I handled_access_net
+is a bitmask of handled network actions
+(see
+.B Network actions
+in
+.BR landlock (7)).
+.IP
 This structure defines a set of
 .IR "handled access rights" ,
 a set of actions on different object types,
@@ -143,8 +151,8 @@ was not a valid address.
 .TP
 .B ENOMSG
 Empty accesses (i.e.,
-.I attr\->handled_access_fs
-is 0).
+.I attr
+did not specify any access rights to restrict).
 .SH STANDARDS
 Linux.
 .SH HISTORY
diff --git a/man/man7/landlock.7 b/man/man7/landlock.7
index 652054f15..52876a3de 100644
--- a/man/man7/landlock.7
+++ b/man/man7/landlock.7
@@ -189,6 +189,19 @@ If multiple requirements are not met, the
 error code takes precedence over
 .BR EXDEV .
 .\"
+.SS Network flags
+These flags enable to restrict a sandboxed process
+to a set of network actions.
+This is supported since the Landlock ABI version 4.
+.P
+The following access rights apply to TCP port numbers:
+.TP
+.B LANDLOCK_ACCESS_NET_BIND_TCP
+Bind a TCP socket to a local port.
+.TP
+.B LANDLOCK_ACCESS_NET_CONNECT_TCP
+Connect an active TCP socket to a remote port.
+.\"
 .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.
@@ -339,6 +352,9 @@ _	_	_
 2	5.19	LANDLOCK_ACCESS_FS_REFER
 _	_	_
 3	6.2	LANDLOCK_ACCESS_FS_TRUNCATE
+_	_	_
+4	6.7	LANDLOCK_ACCESS_NET_BIND_TCP
+\^	\^	LANDLOCK_ACCESS_NET_CONNECT_TCP
 .TE
 .P
 Users should use the Landlock ABI version rather than the kernel version
@@ -439,9 +455,10 @@ and only use the available subset of access rights:
  * numbers hardcoded to keep the example short.
  */
 __u64 landlock_fs_access_rights[] = {
-    (LANDLOCK_ACCESS_FS_MAKE_SYM << 1) \- 1,  /* v1                 */
-    (LANDLOCK_ACCESS_FS_REFER    << 1) \- 1,  /* v2: add "refer"    */
-    (LANDLOCK_ACCESS_FS_TRUNCATE << 1) \- 1,  /* v3: add "truncate" */
+    (LANDLOCK_ACCESS_FS_MAKE_SYM  << 1) \- 1,  /* v1                  */
+    (LANDLOCK_ACCESS_FS_REFER     << 1) \- 1,  /* v2: add "refer"     */
+    (LANDLOCK_ACCESS_FS_TRUNCATE  << 1) \- 1,  /* v3: add "truncate"  */
+    (LANDLOCK_ACCESS_FS_TRUNCATE  << 1) \- 1,  /* v4: TCP support     */
 };
 \&
 int abi = landlock_create_ruleset(NULL, 0,
-- 
2.45.2.1089.g2a221341d9-goog