[PATCH v3 0/1] landlock: Clarify IPC scoping documentation

[PATCH v3 0/1] landlock: Clarify IPC scoping documentation

[Günther Noack]

Hello!

Thank you for your feedback, here is the third version.

Changes in V3:

* Various man page improvements suggested by Alejandro Colomar

* Squashed man page commits 2/3 and 3/3.

* (No changes in the kernel side documentation)

Changes in V2:

* As Mickaël already applied the first commit ("Minor typo and grammar fixes in
  IPC scoping documentation"), this one is left out here.

* Applied remarks by Daniel Burgener, Alejandro Colomar and Mickaël Salaün

* Replaced reference to send(2) with sendto(2), which is slightly more
  appropriate in that place.

—Günther

Günther Noack (1):
  landlock: Clarify IPC scoping documentation

 Documentation/userspace-api/landlock.rst | 45 ++++++++++++------------
 1 file changed, 22 insertions(+), 23 deletions(-)

[PATCH v3 1/1] landlock: Clarify IPC scoping documentation

[Günther Noack]

* Clarify terminology
* Stop mixing the unix(7) and signal(7) aspects in the explanation.

Terminology:

* The *IPC Scope* of a Landlock domain is that Landlock domain and its
  nested domains.
* An *operation* (e.g., signaling, connecting to abstract UDS) is said to
  be *scoped within a domain* when the flag for that operation was set at
  ruleset creation time.  This means that for the purpose of this
  operation, only processes within the domain's IPC scope are reachable.

Signed-off-by: Günther Noack <gnoack@google.com>
---
 Documentation/userspace-api/landlock.rst | 45 ++++++++++++------------
 1 file changed, 22 insertions(+), 23 deletions(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index ad587f53fe41..4832b16deedb 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -317,33 +317,32 @@ IPC scoping
 -----------
 
 Similar to the implicit `Ptrace restrictions`_, we may want to further restrict
-interactions between sandboxes. Each Landlock domain can be explicitly scoped
-for a set of actions by specifying it on a ruleset.  For example, if a
-sandboxed process should not be able to :manpage:`connect(2)` to a
-non-sandboxed process through abstract :manpage:`unix(7)` sockets, we can
-specify such a restriction with ``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``.
-Moreover, if a sandboxed process should not be able to send a signal to a
-non-sandboxed process, we can specify this restriction with
-``LANDLOCK_SCOPE_SIGNAL``.
+interactions between sandboxes.  Therefore, at ruleset creation time, each
+Landlock domain can restrict the scope for certain operations, so that these
+operations can only reach out to processes within the same Landlock domain or in
+a nested Landlock domain (the "scope").
 
-A sandboxed process can connect to a non-sandboxed process when its domain is
-not scoped. If a process's domain is scoped, it can only connect to sockets
-created by processes in the same scope.
-Moreover, if a process is scoped to send signal to a non-scoped process, it can
-only send signals to processes in the same scope.
+The operations which can be scoped are:
 
-A connected datagram socket behaves like a stream socket when its domain is
-scoped, meaning if the domain is scoped after the socket is connected, it can
-still :manpage:`send(2)` data just like a stream socket.  However, in the same
-scenario, a non-connected datagram socket cannot send data (with
-:manpage:`sendto(2)`) outside its scope.
+``LANDLOCK_SCOPE_SIGNAL``
+    This limits the sending of signals to target processes which run within the
+    same or a nested Landlock domain.
 
-A process with a scoped domain can inherit a socket created by a non-scoped
-process. The process cannot connect to this socket since it has a scoped
-domain.
+``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``
+    This limits the set of abstract :manpage:`unix(7)` sockets to which we can
+    :manpage:`connect(2)` to socket addresses which were created by a process in
+    the same or a nested Landlock domain.
 
-IPC scoping does not support exceptions, so if a domain is scoped, no rules can
-be added to allow access to resources or processes outside of the scope.
+    A :manpage:`sendto(2)` on a non-connected datagram socket is treated as if
+    it were doing an implicit :manpage:`connect(2)` and will be blocked if the
+    remote end does not stem from the same or a nested Landlock domain.
+
+    A :manpage:`sendto(2)` on a socket which was previously connected will not
+    be restricted.  This works for both datagram and stream sockets.
+
+IPC scoping does not support exceptions via :manpage:`landlock_add_rule(2)`.
+If an operation is scoped within a domain, no rules can be added to allow access
+to resources or processes outside of the scope.
 
 Truncating files
 ----------------
-- 
2.48.1.711.g2feabab25a-goog

[PATCH man v3 1/2] landlock.7: Copy introductory description of Landlock rules

[Günther Noack]

Copy over the existing wording from kernel documentation, as it was introduced
in Linux commit 51442e8d64bc ("landlock: Document network support").  Landlock
rules are not only about the filesystem any more and the new wording is more
appropriate.

Signed-off-by: Günther Noack <gnoack@google.com>
---
 man/man7/landlock.7 | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/man/man7/landlock.7 b/man/man7/landlock.7
index c6b7272ea..7b7a797ad 100644
--- a/man/man7/landlock.7
+++ b/man/man7/landlock.7
@@ -39,13 +39,23 @@ 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 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 two existing types of rules are:
+.TP
+.B Filesystem rules
+For these rules, the object is a file hierarchy,
+and the related filesystem actions are defined with
+.IR "filesystem access rights" .
+.TP
+.BR "Network rules" " (since ABI v4)"
+For these rules, the object is a TCP port,
+and the related actions are defined with
+.IR "network access rights" .
 .\"
 .SS Filesystem actions
 These flags enable to restrict a sandboxed process to a
-- 
2.48.1.711.g2feabab25a-goog

[PATCH man v3 2/2] landlock.7: Add IPC scoping documentation in line with kernel side

[Günther Noack]

* Move over documentation for ABI version 6 (IPC scoping features)
* Clarify terminology
* Stop mixing the unix(7) and signal(7) aspects in the explanation.

With this ABI version, Landlock can restrict outgoing interactions with
higher-privileged Landlock domains through Abstract Unix Domain sockets and
signals.

Terminology:

* The *IPC Scope* of a Landlock domain is that Landlock domain and its
  nested domains.

* An *operation* (e.g., signaling, connecting to abstract UDS) is said to
  be *scoped within a domain* when the flag for that operation was set at
  ruleset creation time.  This means that for the purpose of this
  operation, only processes within the domain's IPC scope are reachable.

Link: https://lore.kernel.org/all/20250303194510.135506-4-gnoack@google.com/
Signed-off-by: Günther Noack <gnoack@google.com>
---
 man/man7/landlock.7 | 65 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/man/man7/landlock.7 b/man/man7/landlock.7
index 7b7a797ad..aa383860c 100644
--- a/man/man7/landlock.7
+++ b/man/man7/landlock.7
@@ -246,7 +246,8 @@ This access right is available since the fifth version of the Landlock ABI.
 .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
+This is supported since Landlock ABI version 4.
 .P
 The following access rights apply to TCP port numbers:
 .TP
@@ -256,6 +257,24 @@ Bind a TCP socket to a local port.
 .B LANDLOCK_ACCESS_NET_CONNECT_TCP
 Connect an active TCP socket to a remote port.
 .\"
+.SS Scope flags
+These flags enable isolating a sandboxed process from a set of IPC actions.
+Setting a flag for a ruleset will isolate the Landlock domain
+to forbid connections to resources outside the domain.
+.P
+This is supported since Landlock ABI version 6.
+.P
+The following scopes exist:
+.TP
+.B LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET
+Restrict a sandboxed process from connecting to an abstract UNIX socket
+created by a process outside the related Landlock domain
+(e.g., a parent domain or a non-sandboxed process).
+.TP
+.B LANDLOCK_SCOPE_SIGNAL
+Restrict a sandboxed process from sending a signal
+to another process outside the domain.
+.\"
 .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.
@@ -332,6 +351,47 @@ 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.
 .\"
+.SS IPC scoping
+Similar to the implicit
+.BR "Ptrace restrictions" ,
+we may want to further restrict interactions between sandboxes.
+Therefore, at ruleset creation time,
+each Landlock domain can restrict the scope for certain operations,
+so that these operations can only reach out to processes
+within the same Landlock domain or in a nested Landlock domain (the "scope").
+.P
+The operations which can be scoped are:
+.TP
+.B LANDLOCK_SCOPE_SIGNAL
+This limits the sending of signals to target processes
+which run within the same or a nested Landlock domain.
+.TP
+.B LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET
+This limits the set of abstract
+.BR unix (7)
+sockets to which we can
+.BR connect (2)
+to socket addresses which were created
+by a process in the same or a nested Landlock domain.
+.IP
+A
+.BR sendto (2)
+on a non-connected datagram socket is treated as if it were doing an implicit
+.BR connect (2)
+and will be blocked if the remote end does not stem
+from the same or a nested Landlock domain.
+.IP
+A
+.BR sendto (2)
+on a socket which was previously connected will not be restricted.
+This works for both datagram and stream sockets.
+.P
+IPC scoping does not support exceptions via
+.BR landlock_add_rule (2).
+If an operation is scoped within a domain,
+no rules can be added to allow access to
+resources or processes outside of the scope.
+.\"
 .SS Truncating files
 The operations covered by
 .B LANDLOCK_ACCESS_FS_WRITE_FILE
@@ -411,6 +471,9 @@ _	_	_
 \^	\^	LANDLOCK_ACCESS_NET_CONNECT_TCP
 _	_	_
 5	6.10	LANDLOCK_ACCESS_FS_IOCTL_DEV
+_	_	_
+6	6.12	LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET
+\^	\^	LANDLOCK_SCOPE_SIGNAL
 .TE
 .P
 Users should use the Landlock ABI version rather than the kernel version
-- 
2.48.1.711.g2feabab25a-goog

Re: [PATCH v3 0/1] landlock: Clarify IPC scoping documentation

[Alejandro Colomar]

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Hi Günther,

On Mon, Mar 03, 2025 at 08:45:10PM +0100, Günther Noack wrote:
> Hello!
> 
> Thank you for your feedback, here is the third version.
> 
> Changes in V3:
> 
> * Various man page improvements suggested by Alejandro Colomar
> 
> * Squashed man page commits 2/3 and 3/3.
> 
> * (No changes in the kernel side documentation)

Thanks!  Both man-pages patches LGTM and I've applied them both.


Have a lovely day!
Alex

> 
> Changes in V2:
> 
> * As Mickaël already applied the first commit ("Minor typo and grammar fixes in
>   IPC scoping documentation"), this one is left out here.
> 
> * Applied remarks by Daniel Burgener, Alejandro Colomar and Mickaël Salaün
> 
> * Replaced reference to send(2) with sendto(2), which is slightly more
>   appropriate in that place.
> 
> —Günther
> 
> Günther Noack (1):
>   landlock: Clarify IPC scoping documentation
> 
>  Documentation/userspace-api/landlock.rst | 45 ++++++++++++------------
>  1 file changed, 22 insertions(+), 23 deletions(-)
> 

-- 
<https://www.alejandro-colomar.es/>

[-- Attachment #2: signature.asc --]
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Re: [PATCH v3 1/1] landlock: Clarify IPC scoping documentation

[Mickaël Salaün]

Thanks! Applied.

On Mon, Mar 03, 2025 at 08:45:12PM +0100, Günther Noack wrote:
> * Clarify terminology
> * Stop mixing the unix(7) and signal(7) aspects in the explanation.
> 
> Terminology:
> 
> * The *IPC Scope* of a Landlock domain is that Landlock domain and its
>   nested domains.
> * An *operation* (e.g., signaling, connecting to abstract UDS) is said to
>   be *scoped within a domain* when the flag for that operation was set at
>   ruleset creation time.  This means that for the purpose of this
>   operation, only processes within the domain's IPC scope are reachable.
> 
> Signed-off-by: Günther Noack <gnoack@google.com>
> ---
>  Documentation/userspace-api/landlock.rst | 45 ++++++++++++------------
>  1 file changed, 22 insertions(+), 23 deletions(-)
> 
> diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
> index ad587f53fe41..4832b16deedb 100644
> --- a/Documentation/userspace-api/landlock.rst
> +++ b/Documentation/userspace-api/landlock.rst
> @@ -317,33 +317,32 @@ IPC scoping
>  -----------
>  
>  Similar to the implicit `Ptrace restrictions`_, we may want to further restrict
> -interactions between sandboxes. Each Landlock domain can be explicitly scoped
> -for a set of actions by specifying it on a ruleset.  For example, if a
> -sandboxed process should not be able to :manpage:`connect(2)` to a
> -non-sandboxed process through abstract :manpage:`unix(7)` sockets, we can
> -specify such a restriction with ``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``.
> -Moreover, if a sandboxed process should not be able to send a signal to a
> -non-sandboxed process, we can specify this restriction with
> -``LANDLOCK_SCOPE_SIGNAL``.
> +interactions between sandboxes.  Therefore, at ruleset creation time, each
> +Landlock domain can restrict the scope for certain operations, so that these
> +operations can only reach out to processes within the same Landlock domain or in
> +a nested Landlock domain (the "scope").
>  
> -A sandboxed process can connect to a non-sandboxed process when its domain is
> -not scoped. If a process's domain is scoped, it can only connect to sockets
> -created by processes in the same scope.
> -Moreover, if a process is scoped to send signal to a non-scoped process, it can
> -only send signals to processes in the same scope.
> +The operations which can be scoped are:
>  
> -A connected datagram socket behaves like a stream socket when its domain is
> -scoped, meaning if the domain is scoped after the socket is connected, it can
> -still :manpage:`send(2)` data just like a stream socket.  However, in the same
> -scenario, a non-connected datagram socket cannot send data (with
> -:manpage:`sendto(2)`) outside its scope.
> +``LANDLOCK_SCOPE_SIGNAL``
> +    This limits the sending of signals to target processes which run within the
> +    same or a nested Landlock domain.
>  
> -A process with a scoped domain can inherit a socket created by a non-scoped
> -process. The process cannot connect to this socket since it has a scoped
> -domain.
> +``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``
> +    This limits the set of abstract :manpage:`unix(7)` sockets to which we can
> +    :manpage:`connect(2)` to socket addresses which were created by a process in
> +    the same or a nested Landlock domain.
>  
> -IPC scoping does not support exceptions, so if a domain is scoped, no rules can
> -be added to allow access to resources or processes outside of the scope.
> +    A :manpage:`sendto(2)` on a non-connected datagram socket is treated as if
> +    it were doing an implicit :manpage:`connect(2)` and will be blocked if the
> +    remote end does not stem from the same or a nested Landlock domain.
> +
> +    A :manpage:`sendto(2)` on a socket which was previously connected will not
> +    be restricted.  This works for both datagram and stream sockets.
> +
> +IPC scoping does not support exceptions via :manpage:`landlock_add_rule(2)`.
> +If an operation is scoped within a domain, no rules can be added to allow access
> +to resources or processes outside of the scope.
>  
>  Truncating files
>  ----------------
> -- 
> 2.48.1.711.g2feabab25a-goog
> 
> 

Re: [PATCH man v3 1/2] landlock.7: Copy introductory description of Landlock rules

[Alejandro Colomar]

Hi!

On Mon, Mar 03, 2025 at 08:50:29PM +0100, Günther Noack wrote:
> +.P
> +The two existing types of rules are:

BTW, I didn't want to send back the patch for another revision, so I
applied it as is, but this sentence is likely to get outdated at some
point.

I would have removed the "two" from it.  But we'll be able to remove it
when/if it changes.  I'm just mentioning this for future documentation.


Cheers,
Alex

> +.TP
> +.B Filesystem rules
> +For these rules, the object is a file hierarchy,
> +and the related filesystem actions are defined with
> +.IR "filesystem access rights" .
> +.TP
> +.BR "Network rules" " (since ABI v4)"
> +For these rules, the object is a TCP port,
> +and the related actions are defined with
> +.IR "network access rights" .
>  .\"
>  .SS Filesystem actions
>  These flags enable to restrict a sandboxed process to a
> -- 
> 2.48.1.711.g2feabab25a-goog
> 
> 

-- 
<https://www.alejandro-colomar.es/>