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4dd893d832
Add a function for filesystems to call to implement the FS_IOC_MEASURE_VERITY ioctl. This ioctl retrieves the file measurement that fs-verity calculated for the given file and is enforcing for reads; i.e., reads that don't match this hash will fail. This ioctl can be used for authentication or logging of file measurements in userspace. See the "FS_IOC_MEASURE_VERITY" section of Documentation/filesystems/fsverity.rst for the documentation. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com>
58 lines
1.6 KiB
C
58 lines
1.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/measure.c: ioctl to get a verity file's measurement
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*
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* Copyright 2019 Google LLC
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*/
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#include "fsverity_private.h"
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#include <linux/uaccess.h>
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/**
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* fsverity_ioctl_measure() - get a verity file's measurement
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*
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* Retrieve the file measurement that the kernel is enforcing for reads from a
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* verity file. See the "FS_IOC_MEASURE_VERITY" section of
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* Documentation/filesystems/fsverity.rst for the documentation.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
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{
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const struct inode *inode = file_inode(filp);
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struct fsverity_digest __user *uarg = _uarg;
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const struct fsverity_info *vi;
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const struct fsverity_hash_alg *hash_alg;
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struct fsverity_digest arg;
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vi = fsverity_get_info(inode);
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if (!vi)
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return -ENODATA; /* not a verity file */
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hash_alg = vi->tree_params.hash_alg;
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/*
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* The user specifies the digest_size their buffer has space for; we can
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* return the digest if it fits in the available space. We write back
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* the actual size, which may be shorter than the user-specified size.
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*/
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if (get_user(arg.digest_size, &uarg->digest_size))
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return -EFAULT;
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if (arg.digest_size < hash_alg->digest_size)
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return -EOVERFLOW;
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memset(&arg, 0, sizeof(arg));
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arg.digest_algorithm = hash_alg - fsverity_hash_algs;
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arg.digest_size = hash_alg->digest_size;
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if (copy_to_user(uarg, &arg, sizeof(arg)))
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return -EFAULT;
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if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
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