landlock: Add design choices documentation for filesystem access rights

[linux-2.6-microblaze.git] / Documentation / security / landlock.rst

diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst
index 3df68cb..5c77730 100644 (file)
--- a/Documentation/security/landlock.rst
+++ b/Documentation/security/landlock.rst
@@ -7,7 +7,7 @@ Landlock LSM: kernel documentation
 ==================================
 
 :Author: Mickaël Salaün
-:Date: March 2021
+:Date: May 2022
 
 Landlock's goal is to create scoped access-control (i.e. sandboxing).  To
 harden a whole system, this feature should be available to any process,
@@ -42,6 +42,21 @@ Guiding principles for safe access controls
 * Computation related to Landlock operations (e.g. enforcing a ruleset) shall
   only impact the processes requesting them.
 
+Design choices
+==============
+
+Filesystem access rights
+------------------------
+
+All access rights are tied to an inode and what can be accessed through it.
+Reading the content of a directory doesn't imply to be allowed to read the
+content of a listed inode.  Indeed, a file name is local to its parent
+directory, and an inode can be referenced by multiple file names thanks to
+(hard) links.  Being able to unlink a file only has a direct impact on the
+directory, not the unlinked inode.  This is the reason why
+`LANDLOCK_ACCESS_FS_REMOVE_FILE` or `LANDLOCK_ACCESS_FS_REFER` are not allowed
+to be tied to files but only to directories.
+
 Tests
 =====