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
fuse_file_accessed(struct file * file)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
fuse_passthrough_end_write(struct kiocb * iocb,ssize_t ret)21 static void fuse_passthrough_end_write(struct kiocb *iocb, ssize_t ret)
22 {
23 struct inode *inode = file_inode(iocb->ki_filp);
24
25 fuse_write_update_attr(inode, iocb->ki_pos, ret);
26 }
27
fuse_passthrough_read_iter(struct kiocb * iocb,struct iov_iter * iter)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 .accessed = fuse_file_accessed,
38 };
39
40
41 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
42 backing_file, iocb->ki_pos, count);
43
44 if (!count)
45 return 0;
46
47 ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags,
48 &ctx);
49
50 return ret;
51 }
52
fuse_passthrough_write_iter(struct kiocb * iocb,struct iov_iter * iter)53 ssize_t fuse_passthrough_write_iter(struct kiocb *iocb,
54 struct iov_iter *iter)
55 {
56 struct file *file = iocb->ki_filp;
57 struct inode *inode = file_inode(file);
58 struct fuse_file *ff = file->private_data;
59 struct file *backing_file = fuse_file_passthrough(ff);
60 size_t count = iov_iter_count(iter);
61 ssize_t ret;
62 struct backing_file_ctx ctx = {
63 .cred = ff->cred,
64 .end_write = fuse_passthrough_end_write,
65 };
66
67 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
68 backing_file, iocb->ki_pos, count);
69
70 if (!count)
71 return 0;
72
73 inode_lock(inode);
74 ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags,
75 &ctx);
76 inode_unlock(inode);
77
78 return ret;
79 }
80
fuse_passthrough_splice_read(struct file * in,loff_t * ppos,struct pipe_inode_info * pipe,size_t len,unsigned int flags)81 ssize_t fuse_passthrough_splice_read(struct file *in, loff_t *ppos,
82 struct pipe_inode_info *pipe,
83 size_t len, unsigned int flags)
84 {
85 struct fuse_file *ff = in->private_data;
86 struct file *backing_file = fuse_file_passthrough(ff);
87 struct backing_file_ctx ctx = {
88 .cred = ff->cred,
89 .accessed = fuse_file_accessed,
90 };
91 struct kiocb iocb;
92 ssize_t ret;
93
94 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
95 backing_file, *ppos, len, flags);
96
97 init_sync_kiocb(&iocb, in);
98 iocb.ki_pos = *ppos;
99 ret = backing_file_splice_read(backing_file, &iocb, pipe, len, flags, &ctx);
100 *ppos = iocb.ki_pos;
101
102 return ret;
103 }
104
fuse_passthrough_splice_write(struct pipe_inode_info * pipe,struct file * out,loff_t * ppos,size_t len,unsigned int flags)105 ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe,
106 struct file *out, loff_t *ppos,
107 size_t len, unsigned int flags)
108 {
109 struct fuse_file *ff = out->private_data;
110 struct file *backing_file = fuse_file_passthrough(ff);
111 struct inode *inode = file_inode(out);
112 ssize_t ret;
113 struct backing_file_ctx ctx = {
114 .cred = ff->cred,
115 .end_write = fuse_passthrough_end_write,
116 };
117 struct kiocb iocb;
118
119 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
120 backing_file, *ppos, len, flags);
121
122 inode_lock(inode);
123 init_sync_kiocb(&iocb, out);
124 iocb.ki_pos = *ppos;
125 ret = backing_file_splice_write(pipe, backing_file, &iocb, len, flags, &ctx);
126 *ppos = iocb.ki_pos;
127 inode_unlock(inode);
128
129 return ret;
130 }
131
fuse_passthrough_mmap(struct file * file,struct vm_area_struct * vma)132 ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma)
133 {
134 struct fuse_file *ff = file->private_data;
135 struct file *backing_file = fuse_file_passthrough(ff);
136 struct backing_file_ctx ctx = {
137 .cred = ff->cred,
138 .accessed = fuse_file_accessed,
139 };
140
141 pr_debug("%s: backing_file=0x%p, start=%lu, end=%lu\n", __func__,
142 backing_file, vma->vm_start, vma->vm_end);
143
144 return backing_file_mmap(backing_file, vma, &ctx);
145 }
146
fuse_backing_get(struct fuse_backing * fb)147 struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
148 {
149 if (fb && refcount_inc_not_zero(&fb->count))
150 return fb;
151 return NULL;
152 }
153
fuse_backing_free(struct fuse_backing * fb)154 static void fuse_backing_free(struct fuse_backing *fb)
155 {
156 pr_debug("%s: fb=0x%p\n", __func__, fb);
157
158 if (fb->file)
159 fput(fb->file);
160 put_cred(fb->cred);
161 kfree_rcu(fb, rcu);
162 }
163
fuse_backing_put(struct fuse_backing * fb)164 void fuse_backing_put(struct fuse_backing *fb)
165 {
166 if (fb && refcount_dec_and_test(&fb->count))
167 fuse_backing_free(fb);
168 }
169
fuse_backing_files_init(struct fuse_conn * fc)170 void fuse_backing_files_init(struct fuse_conn *fc)
171 {
172 idr_init(&fc->backing_files_map);
173 }
174
fuse_backing_id_alloc(struct fuse_conn * fc,struct fuse_backing * fb)175 static int fuse_backing_id_alloc(struct fuse_conn *fc, struct fuse_backing *fb)
176 {
177 int id;
178
179 idr_preload(GFP_KERNEL);
180 spin_lock(&fc->lock);
181 /* FIXME: xarray might be space inefficient */
182 id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC);
183 spin_unlock(&fc->lock);
184 idr_preload_end();
185
186 WARN_ON_ONCE(id == 0);
187 return id;
188 }
189
fuse_backing_id_remove(struct fuse_conn * fc,int id)190 static struct fuse_backing *fuse_backing_id_remove(struct fuse_conn *fc,
191 int id)
192 {
193 struct fuse_backing *fb;
194
195 spin_lock(&fc->lock);
196 fb = idr_remove(&fc->backing_files_map, id);
197 spin_unlock(&fc->lock);
198
199 return fb;
200 }
201
fuse_backing_id_free(int id,void * p,void * data)202 static int fuse_backing_id_free(int id, void *p, void *data)
203 {
204 struct fuse_backing *fb = p;
205
206 WARN_ON_ONCE(refcount_read(&fb->count) != 1);
207 fuse_backing_free(fb);
208 return 0;
209 }
210
fuse_backing_files_free(struct fuse_conn * fc)211 void fuse_backing_files_free(struct fuse_conn *fc)
212 {
213 idr_for_each(&fc->backing_files_map, fuse_backing_id_free, NULL);
214 idr_destroy(&fc->backing_files_map);
215 }
216
fuse_backing_open(struct fuse_conn * fc,struct fuse_backing_map * map)217 int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
218 {
219 struct file *file;
220 struct super_block *backing_sb;
221 struct fuse_backing *fb = NULL;
222 int res;
223
224 pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags);
225
226 /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
227 res = -EPERM;
228 if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
229 goto out;
230
231 res = -EINVAL;
232 if (map->flags || map->padding)
233 goto out;
234
235 file = fget_raw(map->fd);
236 res = -EBADF;
237 if (!file)
238 goto out;
239
240 /* read/write/splice/mmap passthrough only relevant for regular files */
241 res = d_is_dir(file->f_path.dentry) ? -EISDIR : -EINVAL;
242 if (!d_is_reg(file->f_path.dentry))
243 goto out_fput;
244
245 backing_sb = file_inode(file)->i_sb;
246 res = -ELOOP;
247 if (backing_sb->s_stack_depth >= fc->max_stack_depth)
248 goto out_fput;
249
250 fb = kmalloc(sizeof(struct fuse_backing), GFP_KERNEL);
251 res = -ENOMEM;
252 if (!fb)
253 goto out_fput;
254
255 fb->file = file;
256 fb->cred = prepare_creds();
257 refcount_set(&fb->count, 1);
258
259 res = fuse_backing_id_alloc(fc, fb);
260 if (res < 0) {
261 fuse_backing_free(fb);
262 fb = NULL;
263 }
264
265 out:
266 pr_debug("%s: fb=0x%p, ret=%i\n", __func__, fb, res);
267
268 return res;
269
270 out_fput:
271 fput(file);
272 goto out;
273 }
274
fuse_backing_close(struct fuse_conn * fc,int backing_id)275 int fuse_backing_close(struct fuse_conn *fc, int backing_id)
276 {
277 struct fuse_backing *fb = NULL;
278 int err;
279
280 pr_debug("%s: backing_id=%d\n", __func__, backing_id);
281
282 /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
283 err = -EPERM;
284 if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
285 goto out;
286
287 err = -EINVAL;
288 if (backing_id <= 0)
289 goto out;
290
291 err = -ENOENT;
292 fb = fuse_backing_id_remove(fc, backing_id);
293 if (!fb)
294 goto out;
295
296 fuse_backing_put(fb);
297 err = 0;
298 out:
299 pr_debug("%s: fb=0x%p, err=%i\n", __func__, fb, err);
300
301 return err;
302 }
303
304 /*
305 * Setup passthrough to a backing file.
306 *
307 * Returns an fb object with elevated refcount to be stored in fuse inode.
308 */
fuse_passthrough_open(struct file * file,struct inode * inode,int backing_id)309 struct fuse_backing *fuse_passthrough_open(struct file *file,
310 struct inode *inode,
311 int backing_id)
312 {
313 struct fuse_file *ff = file->private_data;
314 struct fuse_conn *fc = ff->fm->fc;
315 struct fuse_backing *fb = NULL;
316 struct file *backing_file;
317 int err;
318
319 err = -EINVAL;
320 if (backing_id <= 0)
321 goto out;
322
323 rcu_read_lock();
324 fb = idr_find(&fc->backing_files_map, backing_id);
325 fb = fuse_backing_get(fb);
326 rcu_read_unlock();
327
328 err = -ENOENT;
329 if (!fb)
330 goto out;
331
332 /* Allocate backing file per fuse file to store fuse path */
333 backing_file = backing_file_open(&file->f_path, file->f_flags,
334 &fb->file->f_path, fb->cred);
335 err = PTR_ERR(backing_file);
336 if (IS_ERR(backing_file)) {
337 fuse_backing_put(fb);
338 goto out;
339 }
340
341 err = 0;
342 ff->passthrough = backing_file;
343 ff->cred = get_cred(fb->cred);
344 out:
345 pr_debug("%s: backing_id=%d, fb=0x%p, backing_file=0x%p, err=%i\n", __func__,
346 backing_id, fb, ff->passthrough, err);
347
348 return err ? ERR_PTR(err) : fb;
349 }
350
fuse_passthrough_release(struct fuse_file * ff,struct fuse_backing * fb)351 void fuse_passthrough_release(struct fuse_file *ff, struct fuse_backing *fb)
352 {
353 pr_debug("%s: fb=0x%p, backing_file=0x%p\n", __func__,
354 fb, ff->passthrough);
355
356 fput(ff->passthrough);
357 ff->passthrough = NULL;
358 put_cred(ff->cred);
359 ff->cred = NULL;
360 }
361