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![Eric Biggers](/assets/img/avatar_default.png)
Address several issues with the calling convention and documentation of fsverity_get_digest(): - Make it provide the hash algorithm as either a FS_VERITY_HASH_ALG_* value or HASH_ALGO_* value, at the caller's choice, rather than only a HASH_ALGO_* value as it did before. This allows callers to work with the fsverity native algorithm numbers if they want to. HASH_ALGO_* is what IMA uses, but other users (e.g. overlayfs) should use FS_VERITY_HASH_ALG_* to match fsverity-utils and the fsverity UAPI. - Make it return the digest size so that it doesn't need to be looked up separately. Use the return value for this, since 0 works nicely for the "file doesn't have fsverity enabled" case. This also makes it clear that no other errors are possible. - Rename the 'digest' parameter to 'raw_digest' and clearly document that it is only useful in combination with the algorithm ID. This hopefully clears up a point of confusion. - Export it to modules, since overlayfs will need it for checking the fsverity digests of lowerdata files (https://lore.kernel.org/r/dd294a44e8f401e6b5140029d8355f88748cd8fd.1686565330.git.alexl@redhat.com). Acked-by: Mimi Zohar <zohar@linux.ibm.com> # for the IMA piece Link: https://lore.kernel.org/r/20230612190047.59755-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
102 lines
3.2 KiB
C
102 lines
3.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Ioctl to get a verity file's digest
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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 digest
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* @filp: file to get digest of
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* @_uarg: user pointer to fsverity_digest
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*
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* Retrieve the file digest that the kernel is enforcing for reads from a verity
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* 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->file_digest, 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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/**
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* fsverity_get_digest() - get a verity file's digest
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* @inode: inode to get digest of
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* @raw_digest: (out) the raw file digest
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* @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
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* @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
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*
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* Retrieves the fsverity digest of the given file. The file must have been
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* opened at least once since the inode was last loaded into the inode cache;
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* otherwise this function will not recognize when fsverity is enabled.
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*
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* The file's fsverity digest consists of @raw_digest in combination with either
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* @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
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*
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* IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
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* @raw_digest is meaningless without knowing which algorithm it uses! fsverity
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* provides no security guarantee for users who ignore the algorithm ID, even if
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* they use the digest size (since algorithms can share the same digest size).
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*
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* Return: The size of the raw digest in bytes, or 0 if the file doesn't have
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* fsverity enabled.
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*/
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int fsverity_get_digest(struct inode *inode,
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u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
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u8 *alg, enum hash_algo *halg)
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{
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const struct fsverity_info *vi;
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const struct fsverity_hash_alg *hash_alg;
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vi = fsverity_get_info(inode);
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if (!vi)
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return 0; /* not a verity file */
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hash_alg = vi->tree_params.hash_alg;
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memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
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if (alg)
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*alg = hash_alg - fsverity_hash_algs;
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if (halg)
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*halg = hash_alg->algo_id;
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return hash_alg->digest_size;
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}
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EXPORT_SYMBOL_GPL(fsverity_get_digest);
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