1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Ioctl to get a verity file's digest 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #include "fsverity_private.h" 9 10 #include <linux/uaccess.h> 11 12 /** 13 * fsverity_ioctl_measure() - get a verity file's digest 14 * @filp: file to get digest of 15 * @_uarg: user pointer to fsverity_digest 16 * 17 * Retrieve the file digest that the kernel is enforcing for reads from a verity 18 * file. See the "FS_IOC_MEASURE_VERITY" section of 19 * Documentation/filesystems/fsverity.rst for the documentation. 20 * 21 * Return: 0 on success, -errno on failure 22 */ 23 int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) 24 { 25 const struct inode *inode = file_inode(filp); 26 struct fsverity_digest __user *uarg = _uarg; 27 const struct fsverity_info *vi; 28 const struct fsverity_hash_alg *hash_alg; 29 struct fsverity_digest arg; 30 31 vi = fsverity_get_info(inode); 32 if (!vi) 33 return -ENODATA; /* not a verity file */ 34 hash_alg = vi->tree_params.hash_alg; 35 36 /* 37 * The user specifies the digest_size their buffer has space for; we can 38 * return the digest if it fits in the available space. We write back 39 * the actual size, which may be shorter than the user-specified size. 40 */ 41 42 if (get_user(arg.digest_size, &uarg->digest_size)) 43 return -EFAULT; 44 if (arg.digest_size < hash_alg->digest_size) 45 return -EOVERFLOW; 46 47 memset(&arg, 0, sizeof(arg)); 48 arg.digest_algorithm = hash_alg - fsverity_hash_algs; 49 arg.digest_size = hash_alg->digest_size; 50 51 if (copy_to_user(uarg, &arg, sizeof(arg))) 52 return -EFAULT; 53 54 if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size)) 55 return -EFAULT; 56 57 return 0; 58 } 59 EXPORT_SYMBOL_GPL(fsverity_ioctl_measure); 60 61 /** 62 * fsverity_get_digest() - get a verity file's digest 63 * @inode: inode to get digest of 64 * @raw_digest: (out) the raw file digest 65 * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value 66 * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value 67 * 68 * Retrieves the fsverity digest of the given file. The file must have been 69 * opened at least once since the inode was last loaded into the inode cache; 70 * otherwise this function will not recognize when fsverity is enabled. 71 * 72 * The file's fsverity digest consists of @raw_digest in combination with either 73 * @alg or @halg. (The caller can choose which one of @alg or @halg to use.) 74 * 75 * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since 76 * @raw_digest is meaningless without knowing which algorithm it uses! fsverity 77 * provides no security guarantee for users who ignore the algorithm ID, even if 78 * they use the digest size (since algorithms can share the same digest size). 79 * 80 * Return: The size of the raw digest in bytes, or 0 if the file doesn't have 81 * fsverity enabled. 82 */ 83 int fsverity_get_digest(struct inode *inode, 84 u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE], 85 u8 *alg, enum hash_algo *halg) 86 { 87 const struct fsverity_info *vi; 88 const struct fsverity_hash_alg *hash_alg; 89 90 vi = fsverity_get_info(inode); 91 if (!vi) 92 return 0; /* not a verity file */ 93 94 hash_alg = vi->tree_params.hash_alg; 95 memcpy(raw_digest, vi->file_digest, hash_alg->digest_size); 96 if (alg) 97 *alg = hash_alg - fsverity_hash_algs; 98 if (halg) 99 *halg = hash_alg->algo_id; 100 return hash_alg->digest_size; 101 } 102 EXPORT_SYMBOL_GPL(fsverity_get_digest); 103