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Add an ioctl FS_IOC_GET_ENCRYPTION_NONCE which retrieves the nonce from an encrypted file or directory. The nonce is the 16-byte random value stored in the inode's encryption xattr. It is normally used together with the master key to derive the inode's actual encryption key. The nonces are needed by automated tests that verify the correctness of the ciphertext on-disk. Except for the IV_INO_LBLK_64 case, there's no way to replicate a file's ciphertext without knowing that file's nonce. The nonces aren't secret, and the existing ciphertext verification tests in xfstests retrieve them from disk using debugfs or dump.f2fs. But in environments that lack these debugging tools, getting the nonces by manually parsing the filesystem structure would be very hard. To make this important type of testing much easier, let's just add an ioctl that retrieves the nonce. Link: https://lore.kernel.org/r/20200314205052.93294-2-ebiggers@kernel.org Reviewed-by: Theodore Ts'o <tytso@mit.edu> (cherry picked from commit e98ad464750c0894bc560d10503dae8ff90ccdac) Bug: 151100202 Change-Id: Ieef2c57b9257ae38eb2e5c1a018ca6f325bb62dd Signed-off-by: Eric Biggers <ebiggers@google.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.