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Pull integrity updates from James Morris: "This contains a mixture of bug fixes, code cleanup, and new functionality. Of note is the integrity cache locking fix, file change detection, and support for a new EVM portable and immutable signature type. The re-introduction of the integrity cache lock (iint) fixes the problem of attempting to take the i_rwsem shared a second time, when it was previously taken exclusively. Defining atomic flags resolves the original iint/i_rwsem circular locking - accessing the file data vs. modifying the file metadata. Although it fixes the O_DIRECT problem as well, a subsequent patch is needed to remove the explicit O_DIRECT prevention. For performance reasons, detecting when a file has changed and needs to be re-measured, re-appraised, and/or re-audited, was limited to after the last writer has closed, and only if the file data has changed. Detecting file change is based on i_version. For filesystems that do not support i_version, remote filesystems, or userspace filesystems, the file was measured, appraised and/or audited once and never re-evaluated. Now local filesystems, which do not support i_version or are not mounted with the i_version option, assume the file has changed and are required to re-evaluate the file. This change does not address detecting file change on remote or userspace filesystems. Unlike file data signatures, which can be included and distributed in software packages (eg. rpm, deb), the existing EVM signature, which protects the file metadata, could not be included in software packages, as it includes file system specific information (eg. i_ino, possibly the UUID). This pull request defines a new EVM portable and immutable file metadata signature format, which can be included in software packages" * 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: ima/policy: fix parsing of fsuuid ima: Use i_version only when filesystem supports it integrity: remove unneeded initializations in integrity_iint_cache entries ima: log message to module appraisal error ima: pass filename to ima_rdwr_violation_check() ima: Fix line continuation format ima: support new "hash" and "dont_hash" policy actions ima: re-introduce own integrity cache lock EVM: Add support for portable signature format EVM: Allow userland to permit modification of EVM-protected metadata ima: relax requiring a file signature for new files with zero length |
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This directory attempts to document the ABI between the Linux kernel and userspace, and the relative stability of these interfaces. Due to the everchanging nature of Linux, and the differing maturity levels, these interfaces should be used by userspace programs in different ways. We have four different levels of ABI stability, as shown by the four different subdirectories in this location. Interfaces may change levels of stability according to the rules described below. The different levels of stability are: stable/ This directory documents the interfaces that the developer has defined to be stable. Userspace programs are free to use these interfaces with no restrictions, and backward compatibility for them will be guaranteed for at least 2 years. Most interfaces (like syscalls) are expected to never change and always be available. testing/ This directory documents interfaces that are felt to be stable, as the main development of this interface has been completed. The interface can be changed to add new features, but the current interface will not break by doing this, unless grave errors or security problems are found in them. Userspace programs can start to rely on these interfaces, but they must be aware of changes that can occur before these interfaces move to be marked stable. Programs that use these interfaces are strongly encouraged to add their name to the description of these interfaces, so that the kernel developers can easily notify them if any changes occur (see the description of the layout of the files below for details on how to do this.) obsolete/ This directory documents interfaces that are still remaining in the kernel, but are marked to be removed at some later point in time. The description of the interface will document the reason why it is obsolete and when it can be expected to be removed. removed/ This directory contains a list of the old interfaces that have been removed from the kernel. Every file in these directories will contain the following information: What: Short description of the interface Date: Date created KernelVersion: Kernel version this feature first showed up in. Contact: Primary contact for this interface (may be a mailing list) Description: Long description of the interface and how to use it. Users: All users of this interface who wish to be notified when it changes. This is very important for interfaces in the "testing" stage, so that kernel developers can work with userspace developers to ensure that things do not break in ways that are unacceptable. It is also important to get feedback for these interfaces to make sure they are working in a proper way and do not need to be changed further. How things move between levels: Interfaces in stable may move to obsolete, as long as the proper notification is given. Interfaces may be removed from obsolete and the kernel as long as the documented amount of time has gone by. Interfaces in the testing state can move to the stable state when the developers feel they are finished. They cannot be removed from the kernel tree without going through the obsolete state first. It's up to the developer to place their interfaces in the category they wish for it to start out in. Notable bits of non-ABI, which should not under any circumstances be considered stable: - Kconfig. Userspace should not rely on the presence or absence of any particular Kconfig symbol, in /proc/config.gz, in the copy of .config commonly installed to /boot, or in any invocation of the kernel build process. - Kernel-internal symbols. Do not rely on the presence, absence, location, or type of any kernel symbol, either in System.map files or the kernel binary itself. See Documentation/process/stable-api-nonsense.rst.