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The original behavior was to check if the full set of requested accesses was allowed by at least a rule of every relevant layer. This didn't take into account requests for multiple accesses and same-layer rules allowing the union of these accesses in a complementary way. As a result, multiple accesses requested on a file hierarchy matching rules that, together, allowed these accesses, but without a unique rule allowing all of them, was illegitimately denied. This case should be rare in practice and it can only be triggered by the path_rename or file_open hook implementations. For instance, if, for the same layer, a rule allows execution beneath /a/b and another rule allows read beneath /a, requesting access to read and execute at the same time for /a/b should be allowed for this layer. This was an inconsistency because the union of same-layer rule accesses was already allowed if requested once at a time anyway. This fix changes the way allowed accesses are gathered over a path walk. To take into account all these rule accesses, we store in a matrix all layer granting the set of requested accesses, according to the handled accesses. To avoid heap allocation, we use an array on the stack which is 2*13 bytes. A following commit bringing the LANDLOCK_ACCESS_FS_REFER access right will increase this size to reach 112 bytes (2*14*4) in case of link or rename actions. Add a new layout1.layer_rule_unions test to check that accesses from different rules pertaining to the same layer are ORed in a file hierarchy. Also test that it is not the case for rules from different layers. Reviewed-by: Paul Moore <paul@paul-moore.com> Link: https://lore.kernel.org/r/20220506161102.525323-5-mic@digikod.net Cc: stable@vger.kernel.org Signed-off-by: Mickaël Salaün <mic@digikod.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.