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By default, if the opener has CAP_DAC_OVERRIDE, a kernfs file can be opened regardless of RW permissions. Writing to a kernfs file will thus succeed even if permissions are 0000. It's required to restrict the actions that can be performed on a resource group from userspace based on the mode of the resource group. This restriction will be done through a modification of the file permissions. That is, for example, if a resource group is locked then the user cannot add tasks to the resource group. For this restriction through file permissions to work it has to be ensured that the permissions are always respected. To do so the resctrl filesystem is created with the KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK flag that will result in open(2) failing with -EACCESS regardless of CAP_DAC_OVERRIDE if the permission does not have the respective read or write access. Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: fenghua.yu@intel.com Cc: tony.luck@intel.com Cc: vikas.shivappa@linux.intel.com Cc: gavin.hindman@intel.com Cc: jithu.joseph@intel.com Cc: dave.hansen@intel.com Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/26f4fc25f110bfc07c2d2c8b2c4ee904922fedf7.1529706536.git.reinette.chatre@intel.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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.