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The kernel has the ability to restrict the set of hash algorithms it accepts for the security.ima xattr when it appraises files. Define a new IMA policy rule option "appraise_algos=", using the mentioned mechanism to expose a user-toggable policy knob to opt-in to that restriction and select the desired set of algorithms that must be accepted. When a policy rule uses the 'appraise_algos' option, appraisal of a file referenced by that rule will now fail if the digest algorithm employed to hash the file was not one of those explicitly listed in the option. In its absence, any hash algorithm compiled in the kernel will be accepted. For example, on a system where SELinux is properly deployed, the rule appraise func=BPRM_CHECK obj_type=iptables_exec_t \ appraise_algos=sha256,sha384 will block the execution of iptables if the xattr security.ima of its executables were not hashed with either sha256 or sha384. Signed-off-by: THOBY Simon <Simon.THOBY@viveris.fr> Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
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.