| 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
| 2 | /* Large capacity key type |
| 3 | * |
| 4 | * Copyright (C) 2017-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. |
| 5 | * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved. |
| 6 | * Written by David Howells (dhowells@redhat.com) |
| 7 | */ |
| 8 | |
| 9 | #define pr_fmt(fmt) "big_key: "fmt |
| 10 | #include <linux/init.h> |
| 11 | #include <linux/seq_file.h> |
| 12 | #include <linux/file.h> |
| 13 | #include <linux/shmem_fs.h> |
| 14 | #include <linux/err.h> |
| 15 | #include <linux/random.h> |
| 16 | #include <keys/user-type.h> |
| 17 | #include <keys/big_key-type.h> |
| 18 | #include <crypto/chacha20poly1305.h> |
| 19 | |
| 20 | /* |
| 21 | * Layout of key payload words. |
| 22 | */ |
| 23 | struct big_key_payload { |
| 24 | u8 *data; |
| 25 | struct path path; |
| 26 | size_t length; |
| 27 | }; |
| 28 | #define to_big_key_payload(payload) \ |
| 29 | (struct big_key_payload *)((payload).data) |
| 30 | |
| 31 | /* |
| 32 | * If the data is under this limit, there's no point creating a shm file to |
| 33 | * hold it as the permanently resident metadata for the shmem fs will be at |
| 34 | * least as large as the data. |
| 35 | */ |
| 36 | #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry)) |
| 37 | |
| 38 | /* |
| 39 | * big_key defined keys take an arbitrary string as the description and an |
| 40 | * arbitrary blob of data as the payload |
| 41 | */ |
| 42 | struct key_type key_type_big_key = { |
| 43 | .name = "big_key", |
| 44 | .preparse = big_key_preparse, |
| 45 | .free_preparse = big_key_free_preparse, |
| 46 | .instantiate = generic_key_instantiate, |
| 47 | .revoke = big_key_revoke, |
| 48 | .destroy = big_key_destroy, |
| 49 | .describe = big_key_describe, |
| 50 | .read = big_key_read, |
| 51 | .update = big_key_update, |
| 52 | }; |
| 53 | |
| 54 | /* |
| 55 | * Preparse a big key |
| 56 | */ |
| 57 | int big_key_preparse(struct key_preparsed_payload *prep) |
| 58 | { |
| 59 | struct big_key_payload *payload = to_big_key_payload(prep->payload); |
| 60 | struct file *file; |
| 61 | u8 *buf, *enckey; |
| 62 | ssize_t written; |
| 63 | size_t datalen = prep->datalen; |
| 64 | size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE; |
| 65 | int ret; |
| 66 | |
| 67 | BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data)); |
| 68 | |
| 69 | if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data) |
| 70 | return -EINVAL; |
| 71 | |
| 72 | /* Set an arbitrary quota */ |
| 73 | prep->quotalen = 16; |
| 74 | |
| 75 | payload->length = datalen; |
| 76 | |
| 77 | if (datalen > BIG_KEY_FILE_THRESHOLD) { |
| 78 | /* Create a shmem file to store the data in. This will permit the data |
| 79 | * to be swapped out if needed. |
| 80 | * |
| 81 | * File content is stored encrypted with randomly generated key. |
| 82 | * Since the key is random for each file, we can set the nonce |
| 83 | * to zero, provided we never define a ->update() call. |
| 84 | */ |
| 85 | loff_t pos = 0; |
| 86 | |
| 87 | buf = kvmalloc(enclen, GFP_KERNEL); |
| 88 | if (!buf) |
| 89 | return -ENOMEM; |
| 90 | |
| 91 | /* generate random key */ |
| 92 | enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL); |
| 93 | if (!enckey) { |
| 94 | ret = -ENOMEM; |
| 95 | goto error; |
| 96 | } |
| 97 | ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE); |
| 98 | if (unlikely(ret)) |
| 99 | goto err_enckey; |
| 100 | |
| 101 | /* encrypt data */ |
| 102 | chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0, |
| 103 | 0, enckey); |
| 104 | |
| 105 | /* save aligned data to file */ |
| 106 | file = shmem_kernel_file_setup("", enclen, 0); |
| 107 | if (IS_ERR(file)) { |
| 108 | ret = PTR_ERR(file); |
| 109 | goto err_enckey; |
| 110 | } |
| 111 | |
| 112 | written = kernel_write(file, buf, enclen, &pos); |
| 113 | if (written != enclen) { |
| 114 | ret = written; |
| 115 | if (written >= 0) |
| 116 | ret = -EIO; |
| 117 | goto err_fput; |
| 118 | } |
| 119 | |
| 120 | /* Pin the mount and dentry to the key so that we can open it again |
| 121 | * later |
| 122 | */ |
| 123 | payload->data = enckey; |
| 124 | payload->path = file->f_path; |
| 125 | path_get(&payload->path); |
| 126 | fput(file); |
| 127 | kvfree_sensitive(buf, enclen); |
| 128 | } else { |
| 129 | /* Just store the data in a buffer */ |
| 130 | void *data = kmalloc(datalen, GFP_KERNEL); |
| 131 | |
| 132 | if (!data) |
| 133 | return -ENOMEM; |
| 134 | |
| 135 | payload->data = data; |
| 136 | memcpy(data, prep->data, prep->datalen); |
| 137 | } |
| 138 | return 0; |
| 139 | |
| 140 | err_fput: |
| 141 | fput(file); |
| 142 | err_enckey: |
| 143 | kfree_sensitive(enckey); |
| 144 | error: |
| 145 | kvfree_sensitive(buf, enclen); |
| 146 | return ret; |
| 147 | } |
| 148 | |
| 149 | /* |
| 150 | * Clear preparsement. |
| 151 | */ |
| 152 | void big_key_free_preparse(struct key_preparsed_payload *prep) |
| 153 | { |
| 154 | struct big_key_payload *payload = to_big_key_payload(prep->payload); |
| 155 | |
| 156 | if (prep->datalen > BIG_KEY_FILE_THRESHOLD) |
| 157 | path_put(&payload->path); |
| 158 | kfree_sensitive(payload->data); |
| 159 | } |
| 160 | |
| 161 | /* |
| 162 | * dispose of the links from a revoked keyring |
| 163 | * - called with the key sem write-locked |
| 164 | */ |
| 165 | void big_key_revoke(struct key *key) |
| 166 | { |
| 167 | struct big_key_payload *payload = to_big_key_payload(key->payload); |
| 168 | |
| 169 | /* clear the quota */ |
| 170 | key_payload_reserve(key, 0); |
| 171 | if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD) |
| 172 | vfs_truncate(&payload->path, 0); |
| 173 | } |
| 174 | |
| 175 | /* |
| 176 | * dispose of the data dangling from the corpse of a big_key key |
| 177 | */ |
| 178 | void big_key_destroy(struct key *key) |
| 179 | { |
| 180 | struct big_key_payload *payload = to_big_key_payload(key->payload); |
| 181 | |
| 182 | if (payload->length > BIG_KEY_FILE_THRESHOLD) { |
| 183 | path_put(&payload->path); |
| 184 | payload->path.mnt = NULL; |
| 185 | payload->path.dentry = NULL; |
| 186 | } |
| 187 | kfree_sensitive(payload->data); |
| 188 | payload->data = NULL; |
| 189 | } |
| 190 | |
| 191 | /* |
| 192 | * Update a big key |
| 193 | */ |
| 194 | int big_key_update(struct key *key, struct key_preparsed_payload *prep) |
| 195 | { |
| 196 | int ret; |
| 197 | |
| 198 | ret = key_payload_reserve(key, prep->datalen); |
| 199 | if (ret < 0) |
| 200 | return ret; |
| 201 | |
| 202 | if (key_is_positive(key)) |
| 203 | big_key_destroy(key); |
| 204 | |
| 205 | return generic_key_instantiate(key, prep); |
| 206 | } |
| 207 | |
| 208 | /* |
| 209 | * describe the big_key key |
| 210 | */ |
| 211 | void big_key_describe(const struct key *key, struct seq_file *m) |
| 212 | { |
| 213 | struct big_key_payload *payload = to_big_key_payload(key->payload); |
| 214 | |
| 215 | seq_puts(m, key->description); |
| 216 | |
| 217 | if (key_is_positive(key)) |
| 218 | seq_printf(m, ": %zu [%s]", |
| 219 | payload->length, |
| 220 | payload->length > BIG_KEY_FILE_THRESHOLD ? "file" : "buff"); |
| 221 | } |
| 222 | |
| 223 | /* |
| 224 | * read the key data |
| 225 | * - the key's semaphore is read-locked |
| 226 | */ |
| 227 | long big_key_read(const struct key *key, char *buffer, size_t buflen) |
| 228 | { |
| 229 | struct big_key_payload *payload = to_big_key_payload(key->payload); |
| 230 | size_t datalen = payload->length; |
| 231 | long ret; |
| 232 | |
| 233 | if (!buffer || buflen < datalen) |
| 234 | return datalen; |
| 235 | |
| 236 | if (datalen > BIG_KEY_FILE_THRESHOLD) { |
| 237 | struct file *file; |
| 238 | u8 *buf, *enckey = payload->data; |
| 239 | size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE; |
| 240 | loff_t pos = 0; |
| 241 | |
| 242 | buf = kvmalloc(enclen, GFP_KERNEL); |
| 243 | if (!buf) |
| 244 | return -ENOMEM; |
| 245 | |
| 246 | file = dentry_open(&payload->path, O_RDONLY, current_cred()); |
| 247 | if (IS_ERR(file)) { |
| 248 | ret = PTR_ERR(file); |
| 249 | goto error; |
| 250 | } |
| 251 | |
| 252 | /* read file to kernel and decrypt */ |
| 253 | ret = kernel_read(file, buf, enclen, &pos); |
| 254 | if (ret != enclen) { |
| 255 | if (ret >= 0) |
| 256 | ret = -EIO; |
| 257 | goto err_fput; |
| 258 | } |
| 259 | |
| 260 | ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0, |
| 261 | enckey) ? 0 : -EBADMSG; |
| 262 | if (unlikely(ret)) |
| 263 | goto err_fput; |
| 264 | |
| 265 | ret = datalen; |
| 266 | |
| 267 | /* copy out decrypted data */ |
| 268 | memcpy(buffer, buf, datalen); |
| 269 | |
| 270 | err_fput: |
| 271 | fput(file); |
| 272 | error: |
| 273 | kvfree_sensitive(buf, enclen); |
| 274 | } else { |
| 275 | ret = datalen; |
| 276 | memcpy(buffer, payload->data, datalen); |
| 277 | } |
| 278 | |
| 279 | return ret; |
| 280 | } |
| 281 | |
| 282 | /* |
| 283 | * Register key type |
| 284 | */ |
| 285 | static int __init big_key_init(void) |
| 286 | { |
| 287 | return register_key_type(&key_type_big_key); |
| 288 | } |
| 289 | |
| 290 | late_initcall(big_key_init); |