1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * FUSE passthrough to backing file.
4 *
5 * Copyright (c) 2023 CTERA Networks.
6 */
7
8 #include "fuse_i.h"
9
10 #include <linux/file.h>
11 #include <linux/backing-file.h>
12 #include <linux/splice.h>
13
14 static void fuse_file_accessed(struct file *file)
15 {
16 struct inode *inode = file_inode(file);
17
18 fuse_invalidate_atime(inode);
19 }
20
21 static void fuse_file_modified(struct file *file)
22 {
23 struct inode *inode = file_inode(file);
24
25 fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
26 }
27
28 ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter)
29 {
30 struct file *file = iocb->ki_filp;
31 struct fuse_file *ff = file->private_data;
32 struct file *backing_file = fuse_file_passthrough(ff);
33 size_t count = iov_iter_count(iter);
34 ssize_t ret;
35 struct backing_file_ctx ctx = {
36 .cred = ff->cred,
37 .user_file = file,
38 .accessed = fuse_file_accessed,
39 };
40
41
42 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
43 backing_file, iocb->ki_pos, count);
44
45 if (!count)
46 return 0;
47
48 ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags,
49 &ctx);
50
51 return ret;
52 }
53
54 ssize_t fuse_passthrough_write_iter(struct kiocb *iocb,
55 struct iov_iter *iter)
56 {
57 struct file *file = iocb->ki_filp;
58 struct inode *inode = file_inode(file);
59 struct fuse_file *ff = file->private_data;
60 struct file *backing_file = fuse_file_passthrough(ff);
61 size_t count = iov_iter_count(iter);
62 ssize_t ret;
63 struct backing_file_ctx ctx = {
64 .cred = ff->cred,
65 .user_file = file,
66 .end_write = fuse_file_modified,
67 };
68
69 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
70 backing_file, iocb->ki_pos, count);
71
72 if (!count)
73 return 0;
74
75 inode_lock(inode);
76 ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags,
77 &ctx);
78 inode_unlock(inode);
79
80 return ret;
81 }
82
83 ssize_t fuse_passthrough_splice_read(struct file *in, loff_t *ppos,
84 struct pipe_inode_info *pipe,
85 size_t len, unsigned int flags)
86 {
87 struct fuse_file *ff = in->private_data;
88 struct file *backing_file = fuse_file_passthrough(ff);
89 struct backing_file_ctx ctx = {
90 .cred = ff->cred,
91 .user_file = in,
92 .accessed = fuse_file_accessed,
93 };
94
95 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
96 backing_file, ppos ? *ppos : 0, len, flags);
97
98 return backing_file_splice_read(backing_file, ppos, pipe, len, flags,
99 &ctx);
100 }
101
102 ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe,
103 struct file *out, loff_t *ppos,
104 size_t len, unsigned int flags)
105 {
106 struct fuse_file *ff = out->private_data;
107 struct file *backing_file = fuse_file_passthrough(ff);
108 struct inode *inode = file_inode(out);
109 ssize_t ret;
110 struct backing_file_ctx ctx = {
111 .cred = ff->cred,
112 .user_file = out,
113 .end_write = fuse_file_modified,
114 };
115
116 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
117 backing_file, ppos ? *ppos : 0, len, flags);
118
119 inode_lock(inode);
120 ret = backing_file_splice_write(pipe, backing_file, ppos, len, flags,
121 &ctx);
122 inode_unlock(inode);
123
124 return ret;
125 }
126
127 ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma)
128 {
129 struct fuse_file *ff = file->private_data;
130 struct file *backing_file = fuse_file_passthrough(ff);
131 struct backing_file_ctx ctx = {
132 .cred = ff->cred,
133 .user_file = file,
134 .accessed = fuse_file_accessed,
135 };
136
137 pr_debug("%s: backing_file=0x%p, start=%lu, end=%lu\n", __func__,
138 backing_file, vma->vm_start, vma->vm_end);
139
140 return backing_file_mmap(backing_file, vma, &ctx);
141 }
142
143 struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
144 {
145 if (fb && refcount_inc_not_zero(&fb->count))
146 return fb;
147 return NULL;
148 }
149
150 static void fuse_backing_free(struct fuse_backing *fb)
151 {
152 pr_debug("%s: fb=0x%p\n", __func__, fb);
153
154 if (fb->file)
155 fput(fb->file);
156 put_cred(fb->cred);
157 kfree_rcu(fb, rcu);
158 }
159
160 void fuse_backing_put(struct fuse_backing *fb)
161 {
162 if (fb && refcount_dec_and_test(&fb->count))
163 fuse_backing_free(fb);
164 }
165
166 void fuse_backing_files_init(struct fuse_conn *fc)
167 {
168 idr_init(&fc->backing_files_map);
169 }
170
171 static int fuse_backing_id_alloc(struct fuse_conn *fc, struct fuse_backing *fb)
172 {
173 int id;
174
175 idr_preload(GFP_KERNEL);
176 spin_lock(&fc->lock);
177 /* FIXME: xarray might be space inefficient */
178 id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC);
179 spin_unlock(&fc->lock);
180 idr_preload_end();
181
182 WARN_ON_ONCE(id == 0);
183 return id;
184 }
185
186 static struct fuse_backing *fuse_backing_id_remove(struct fuse_conn *fc,
187 int id)
188 {
189 struct fuse_backing *fb;
190
191 spin_lock(&fc->lock);
192 fb = idr_remove(&fc->backing_files_map, id);
193 spin_unlock(&fc->lock);
194
195 return fb;
196 }
197
198 static int fuse_backing_id_free(int id, void *p, void *data)
199 {
200 struct fuse_backing *fb = p;
201
202 WARN_ON_ONCE(refcount_read(&fb->count) != 1);
203 fuse_backing_free(fb);
204 return 0;
205 }
206
207 void fuse_backing_files_free(struct fuse_conn *fc)
208 {
209 idr_for_each(&fc->backing_files_map, fuse_backing_id_free, NULL);
210 idr_destroy(&fc->backing_files_map);
211 }
212
213 int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
214 {
215 struct file *file;
216 struct super_block *backing_sb;
217 struct fuse_backing *fb = NULL;
218 int res;
219
220 pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags);
221
222 /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
223 res = -EPERM;
224 if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
225 goto out;
226
227 res = -EINVAL;
228 if (map->flags || map->padding)
229 goto out;
230
231 file = fget(map->fd);
232 res = -EBADF;
233 if (!file)
234 goto out;
235
236 res = -EOPNOTSUPP;
237 if (!file->f_op->read_iter || !file->f_op->write_iter)
238 goto out_fput;
239
240 backing_sb = file_inode(file)->i_sb;
241 res = -ELOOP;
242 if (backing_sb->s_stack_depth >= fc->max_stack_depth)
243 goto out_fput;
244
245 fb = kmalloc(sizeof(struct fuse_backing), GFP_KERNEL);
246 res = -ENOMEM;
247 if (!fb)
248 goto out_fput;
249
250 fb->file = file;
251 fb->cred = prepare_creds();
252 refcount_set(&fb->count, 1);
253
254 res = fuse_backing_id_alloc(fc, fb);
255 if (res < 0) {
256 fuse_backing_free(fb);
257 fb = NULL;
258 }
259
260 out:
261 pr_debug("%s: fb=0x%p, ret=%i\n", __func__, fb, res);
262
263 return res;
264
265 out_fput:
266 fput(file);
267 goto out;
268 }
269
270 int fuse_backing_close(struct fuse_conn *fc, int backing_id)
271 {
272 struct fuse_backing *fb = NULL;
273 int err;
274
275 pr_debug("%s: backing_id=%d\n", __func__, backing_id);
276
277 /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
278 err = -EPERM;
279 if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
280 goto out;
281
282 err = -EINVAL;
283 if (backing_id <= 0)
284 goto out;
285
286 err = -ENOENT;
287 fb = fuse_backing_id_remove(fc, backing_id);
288 if (!fb)
289 goto out;
290
291 fuse_backing_put(fb);
292 err = 0;
293 out:
294 pr_debug("%s: fb=0x%p, err=%i\n", __func__, fb, err);
295
296 return err;
297 }
298
299 /*
300 * Setup passthrough to a backing file.
301 *
302 * Returns an fb object with elevated refcount to be stored in fuse inode.
303 */
304 struct fuse_backing *fuse_passthrough_open(struct file *file,
305 struct inode *inode,
306 int backing_id)
307 {
308 struct fuse_file *ff = file->private_data;
309 struct fuse_conn *fc = ff->fm->fc;
310 struct fuse_backing *fb = NULL;
311 struct file *backing_file;
312 int err;
313
314 err = -EINVAL;
315 if (backing_id <= 0)
316 goto out;
317
318 rcu_read_lock();
319 fb = idr_find(&fc->backing_files_map, backing_id);
320 fb = fuse_backing_get(fb);
321 rcu_read_unlock();
322
323 err = -ENOENT;
324 if (!fb)
325 goto out;
326
327 /* Allocate backing file per fuse file to store fuse path */
328 backing_file = backing_file_open(&file->f_path, file->f_flags,
329 &fb->file->f_path, fb->cred);
330 err = PTR_ERR(backing_file);
331 if (IS_ERR(backing_file)) {
332 fuse_backing_put(fb);
333 goto out;
334 }
335
336 err = 0;
337 ff->passthrough = backing_file;
338 ff->cred = get_cred(fb->cred);
339 out:
340 pr_debug("%s: backing_id=%d, fb=0x%p, backing_file=0x%p, err=%i\n", __func__,
341 backing_id, fb, ff->passthrough, err);
342
343 return err ? ERR_PTR(err) : fb;
344 }
345
346 void fuse_passthrough_release(struct fuse_file *ff, struct fuse_backing *fb)
347 {
348 pr_debug("%s: fb=0x%p, backing_file=0x%p\n", __func__,
349 fb, ff->passthrough);
350
351 fput(ff->passthrough);
352 ff->passthrough = NULL;
353 put_cred(ff->cred);
354 ff->cred = NULL;
355 }
356
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.