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// SPDX-License-Identifier: GPL-2.0
/*
* Ioctl to get a verity file's digest
*
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
#include <linux/uaccess.h>
/**
* fsverity_ioctl_measure() - get a verity file's digest
* @filp: file to get digest of
* @_uarg: user pointer to fsverity_digest
*
* Retrieve the file digest that the kernel is enforcing for reads from a verity
* file. See the "FS_IOC_MEASURE_VERITY" section of
* Documentation/filesystems/fsverity.rst for the documentation.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
{
const struct inode *inode = file_inode(filp);
struct fsverity_digest __user *uarg = _uarg;
const struct fsverity_info *vi;
const struct fsverity_hash_alg *hash_alg;
struct fsverity_digest arg;
vi = fsverity_get_info(inode);
if (!vi)
return -ENODATA; /* not a verity file */
hash_alg = vi->tree_params.hash_alg;
/*
* The user specifies the digest_size their buffer has space for; we can
* return the digest if it fits in the available space. We write back
* the actual size, which may be shorter than the user-specified size.
*/
if (get_user(arg.digest_size, &uarg->digest_size))
return -EFAULT;
if (arg.digest_size < hash_alg->digest_size)
return -EOVERFLOW;
memset(&arg, 0, sizeof(arg));
arg.digest_algorithm = hash_alg - fsverity_hash_algs;
arg.digest_size = hash_alg->digest_size;
if (copy_to_user(uarg, &arg, sizeof(arg)))
return -EFAULT;
if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
return -EFAULT;
return 0;
}
EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
/**
* fsverity_get_digest() - get a verity file's digest
* @inode: inode to get digest of
* @raw_digest: (out) the raw file digest
* @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
* @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
*
* Retrieves the fsverity digest of the given file. The file must have been
* opened at least once since the inode was last loaded into the inode cache;
* otherwise this function will not recognize when fsverity is enabled.
*
* The file's fsverity digest consists of @raw_digest in combination with either
* @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
*
* IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
* @raw_digest is meaningless without knowing which algorithm it uses! fsverity
* provides no security guarantee for users who ignore the algorithm ID, even if
* they use the digest size (since algorithms can share the same digest size).
*
* Return: The size of the raw digest in bytes, or 0 if the file doesn't have
* fsverity enabled.
*/
int fsverity_get_digest(struct inode *inode,
u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
u8 *alg, enum hash_algo *halg)
{
const struct fsverity_info *vi;
const struct fsverity_hash_alg *hash_alg;
vi = fsverity_get_info(inode);
if (!vi)
return 0; /* not a verity file */
hash_alg = vi->tree_params.hash_alg;
memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
if (alg)
*alg = hash_alg - fsverity_hash_algs;
if (halg)
*halg = hash_alg->algo_id;
return hash_alg->digest_size;
}
EXPORT_SYMBOL_GPL(fsverity_get_digest);
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