81ff94442f7b48daabd0d1e6604cda422735f413
[releases.git] / open.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Opening fs-verity files
4  *
5  * Copyright 2019 Google LLC
6  */
7
8 #include "fsverity_private.h"
9
10 #include <linux/slab.h>
11
12 static struct kmem_cache *fsverity_info_cachep;
13
14 /**
15  * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
16  * @params: the parameters struct to initialize
17  * @inode: the inode for which the Merkle tree is being built
18  * @hash_algorithm: number of hash algorithm to use
19  * @log_blocksize: log base 2 of block size to use
20  * @salt: pointer to salt (optional)
21  * @salt_size: size of salt, possibly 0
22  *
23  * Validate the hash algorithm and block size, then compute the tree topology
24  * (num levels, num blocks in each level, etc.) and initialize @params.
25  *
26  * Return: 0 on success, -errno on failure
27  */
28 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
29                                      const struct inode *inode,
30                                      unsigned int hash_algorithm,
31                                      unsigned int log_blocksize,
32                                      const u8 *salt, size_t salt_size)
33 {
34         struct fsverity_hash_alg *hash_alg;
35         int err;
36         u64 blocks;
37         u64 offset;
38         int level;
39
40         memset(params, 0, sizeof(*params));
41
42         hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
43         if (IS_ERR(hash_alg))
44                 return PTR_ERR(hash_alg);
45         params->hash_alg = hash_alg;
46         params->digest_size = hash_alg->digest_size;
47
48         params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
49                                                         salt_size);
50         if (IS_ERR(params->hashstate)) {
51                 err = PTR_ERR(params->hashstate);
52                 params->hashstate = NULL;
53                 fsverity_err(inode, "Error %d preparing hash state", err);
54                 goto out_err;
55         }
56
57         if (log_blocksize != PAGE_SHIFT) {
58                 fsverity_warn(inode, "Unsupported log_blocksize: %u",
59                               log_blocksize);
60                 err = -EINVAL;
61                 goto out_err;
62         }
63         params->log_blocksize = log_blocksize;
64         params->block_size = 1 << log_blocksize;
65
66         if (WARN_ON(!is_power_of_2(params->digest_size))) {
67                 err = -EINVAL;
68                 goto out_err;
69         }
70         if (params->block_size < 2 * params->digest_size) {
71                 fsverity_warn(inode,
72                               "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
73                               params->block_size, hash_alg->name);
74                 err = -EINVAL;
75                 goto out_err;
76         }
77         params->log_arity = params->log_blocksize - ilog2(params->digest_size);
78         params->hashes_per_block = 1 << params->log_arity;
79
80         pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
81                  hash_alg->name, params->block_size, params->hashes_per_block,
82                  (int)salt_size, salt);
83
84         /*
85          * Compute the number of levels in the Merkle tree and create a map from
86          * level to the starting block of that level.  Level 'num_levels - 1' is
87          * the root and is stored first.  Level 0 is the level directly "above"
88          * the data blocks and is stored last.
89          */
90
91         /* Compute number of levels and the number of blocks in each level */
92         blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
93         pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
94         while (blocks > 1) {
95                 if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
96                         fsverity_err(inode, "Too many levels in Merkle tree");
97                         err = -EINVAL;
98                         goto out_err;
99                 }
100                 blocks = (blocks + params->hashes_per_block - 1) >>
101                          params->log_arity;
102                 /* temporarily using level_start[] to store blocks in level */
103                 params->level_start[params->num_levels++] = blocks;
104         }
105         params->level0_blocks = params->level_start[0];
106
107         /* Compute the starting block of each level */
108         offset = 0;
109         for (level = (int)params->num_levels - 1; level >= 0; level--) {
110                 blocks = params->level_start[level];
111                 params->level_start[level] = offset;
112                 pr_debug("Level %d is %llu blocks starting at index %llu\n",
113                          level, blocks, offset);
114                 offset += blocks;
115         }
116
117         params->tree_size = offset << log_blocksize;
118         return 0;
119
120 out_err:
121         kfree(params->hashstate);
122         memset(params, 0, sizeof(*params));
123         return err;
124 }
125
126 /*
127  * Compute the file digest by hashing the fsverity_descriptor excluding the
128  * signature and with the sig_size field set to 0.
129  */
130 static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
131                                struct fsverity_descriptor *desc,
132                                u8 *file_digest)
133 {
134         __le32 sig_size = desc->sig_size;
135         int err;
136
137         desc->sig_size = 0;
138         err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
139         desc->sig_size = sig_size;
140
141         return err;
142 }
143
144 /*
145  * Create a new fsverity_info from the given fsverity_descriptor (with optional
146  * appended signature), and check the signature if present.  The
147  * fsverity_descriptor must have already undergone basic validation.
148  */
149 struct fsverity_info *fsverity_create_info(const struct inode *inode,
150                                            struct fsverity_descriptor *desc)
151 {
152         struct fsverity_info *vi;
153         int err;
154
155         vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
156         if (!vi)
157                 return ERR_PTR(-ENOMEM);
158         vi->inode = inode;
159
160         err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
161                                                desc->hash_algorithm,
162                                                desc->log_blocksize,
163                                                desc->salt, desc->salt_size);
164         if (err) {
165                 fsverity_err(inode,
166                              "Error %d initializing Merkle tree parameters",
167                              err);
168                 goto out;
169         }
170
171         memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
172
173         err = compute_file_digest(vi->tree_params.hash_alg, desc,
174                                   vi->file_digest);
175         if (err) {
176                 fsverity_err(inode, "Error %d computing file digest", err);
177                 goto out;
178         }
179         pr_debug("Computed file digest: %s:%*phN\n",
180                  vi->tree_params.hash_alg->name,
181                  vi->tree_params.digest_size, vi->file_digest);
182
183         err = fsverity_verify_signature(vi, desc->signature,
184                                         le32_to_cpu(desc->sig_size));
185 out:
186         if (err) {
187                 fsverity_free_info(vi);
188                 vi = ERR_PTR(err);
189         }
190         return vi;
191 }
192
193 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
194 {
195         /*
196          * Multiple tasks may race to set ->i_verity_info, so use
197          * cmpxchg_release().  This pairs with the smp_load_acquire() in
198          * fsverity_get_info().  I.e., here we publish ->i_verity_info with a
199          * RELEASE barrier so that other tasks can ACQUIRE it.
200          */
201         if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
202                 /* Lost the race, so free the fsverity_info we allocated. */
203                 fsverity_free_info(vi);
204                 /*
205                  * Afterwards, the caller may access ->i_verity_info directly,
206                  * so make sure to ACQUIRE the winning fsverity_info.
207                  */
208                 (void)fsverity_get_info(inode);
209         }
210 }
211
212 void fsverity_free_info(struct fsverity_info *vi)
213 {
214         if (!vi)
215                 return;
216         kfree(vi->tree_params.hashstate);
217         kmem_cache_free(fsverity_info_cachep, vi);
218 }
219
220 static bool validate_fsverity_descriptor(struct inode *inode,
221                                          const struct fsverity_descriptor *desc,
222                                          size_t desc_size)
223 {
224         if (desc_size < sizeof(*desc)) {
225                 fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
226                              desc_size);
227                 return false;
228         }
229
230         if (desc->version != 1) {
231                 fsverity_err(inode, "Unrecognized descriptor version: %u",
232                              desc->version);
233                 return false;
234         }
235
236         if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
237                 fsverity_err(inode, "Reserved bits set in descriptor");
238                 return false;
239         }
240
241         if (desc->salt_size > sizeof(desc->salt)) {
242                 fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
243                 return false;
244         }
245
246         if (le64_to_cpu(desc->data_size) != inode->i_size) {
247                 fsverity_err(inode,
248                              "Wrong data_size: %llu (desc) != %lld (inode)",
249                              le64_to_cpu(desc->data_size), inode->i_size);
250                 return false;
251         }
252
253         if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
254                 fsverity_err(inode, "Signature overflows verity descriptor");
255                 return false;
256         }
257
258         return true;
259 }
260
261 /*
262  * Read the inode's fsverity_descriptor (with optional appended signature) from
263  * the filesystem, and do basic validation of it.
264  */
265 int fsverity_get_descriptor(struct inode *inode,
266                             struct fsverity_descriptor **desc_ret)
267 {
268         int res;
269         struct fsverity_descriptor *desc;
270
271         res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
272         if (res < 0) {
273                 fsverity_err(inode,
274                              "Error %d getting verity descriptor size", res);
275                 return res;
276         }
277         if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
278                 fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
279                              res);
280                 return -EMSGSIZE;
281         }
282         desc = kmalloc(res, GFP_KERNEL);
283         if (!desc)
284                 return -ENOMEM;
285         res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
286         if (res < 0) {
287                 fsverity_err(inode, "Error %d reading verity descriptor", res);
288                 kfree(desc);
289                 return res;
290         }
291
292         if (!validate_fsverity_descriptor(inode, desc, res)) {
293                 kfree(desc);
294                 return -EINVAL;
295         }
296
297         *desc_ret = desc;
298         return 0;
299 }
300
301 /* Ensure the inode has an ->i_verity_info */
302 static int ensure_verity_info(struct inode *inode)
303 {
304         struct fsverity_info *vi = fsverity_get_info(inode);
305         struct fsverity_descriptor *desc;
306         int err;
307
308         if (vi)
309                 return 0;
310
311         err = fsverity_get_descriptor(inode, &desc);
312         if (err)
313                 return err;
314
315         vi = fsverity_create_info(inode, desc);
316         if (IS_ERR(vi)) {
317                 err = PTR_ERR(vi);
318                 goto out_free_desc;
319         }
320
321         fsverity_set_info(inode, vi);
322         err = 0;
323 out_free_desc:
324         kfree(desc);
325         return err;
326 }
327
328 /**
329  * fsverity_file_open() - prepare to open a verity file
330  * @inode: the inode being opened
331  * @filp: the struct file being set up
332  *
333  * When opening a verity file, deny the open if it is for writing.  Otherwise,
334  * set up the inode's ->i_verity_info if not already done.
335  *
336  * When combined with fscrypt, this must be called after fscrypt_file_open().
337  * Otherwise, we won't have the key set up to decrypt the verity metadata.
338  *
339  * Return: 0 on success, -errno on failure
340  */
341 int fsverity_file_open(struct inode *inode, struct file *filp)
342 {
343         if (!IS_VERITY(inode))
344                 return 0;
345
346         if (filp->f_mode & FMODE_WRITE) {
347                 pr_debug("Denying opening verity file (ino %lu) for write\n",
348                          inode->i_ino);
349                 return -EPERM;
350         }
351
352         return ensure_verity_info(inode);
353 }
354 EXPORT_SYMBOL_GPL(fsverity_file_open);
355
356 /**
357  * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
358  * @dentry: dentry through which the inode is being changed
359  * @attr: attributes to change
360  *
361  * Verity files are immutable, so deny truncates.  This isn't covered by the
362  * open-time check because sys_truncate() takes a path, not a file descriptor.
363  *
364  * Return: 0 on success, -errno on failure
365  */
366 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
367 {
368         if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
369                 pr_debug("Denying truncate of verity file (ino %lu)\n",
370                          d_inode(dentry)->i_ino);
371                 return -EPERM;
372         }
373         return 0;
374 }
375 EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
376
377 /**
378  * fsverity_cleanup_inode() - free the inode's verity info, if present
379  * @inode: an inode being evicted
380  *
381  * Filesystems must call this on inode eviction to free ->i_verity_info.
382  */
383 void fsverity_cleanup_inode(struct inode *inode)
384 {
385         fsverity_free_info(inode->i_verity_info);
386         inode->i_verity_info = NULL;
387 }
388 EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
389
390 int __init fsverity_init_info_cache(void)
391 {
392         fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
393                                                    SLAB_RECLAIM_ACCOUNT,
394                                                    file_digest);
395         if (!fsverity_info_cachep)
396                 return -ENOMEM;
397         return 0;
398 }
399
400 void __init fsverity_exit_info_cache(void)
401 {
402         kmem_cache_destroy(fsverity_info_cachep);
403         fsverity_info_cachep = NULL;
404 }