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From:   =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@digikod.net>
To:     James Morris <jmorris@namei.org>,
        "Serge E . Hallyn" <serge@hallyn.com>
Cc:     =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@digikod.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jann Horn <jannh@google.com>,
        John Johansen <john.johansen@canonical.com>,
        Kees Cook <keescook@chromium.org>,
        Konstantin Meskhidze <konstantin.meskhidze@huawei.com>,
        Paul Moore <paul@paul-moore.com>,
        Shuah Khan <shuah@kernel.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org
Subject: [PATCH v3 12/12] landlock: Add design choices documentation for filesystem access rights
Date:   Fri,  6 May 2022 18:11:02 +0200
Message-Id: <20220506161102.525323-13-mic@digikod.net>
In-Reply-To: <20220506161102.525323-1-mic@digikod.net>
References: <20220506161102.525323-1-mic@digikod.net>
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Summarize the rationale of filesystem access rights according to the
file type.

Update the document date.

Reviewed-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506161102.525323-13-mic@digikod.net
---

Changes since v2:
* Add more explanation in the commit message.
* Update date.

Changes since v1:
* Add Reviewed-by: Paul Moore.
* Update date.
---
 Documentation/security/landlock.rst | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst
index 3df68cb1d10f..5c77730b4479 100644
--- 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
 =====
 
-- 
2.35.1