1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Common helpers for stackable filesystems and backing files.
4 *
5 * Forked from fs/overlayfs/file.c.
6 *
7 * Copyright (C) 2017 Red Hat, Inc.
8 * Copyright (C) 2023 CTERA Networks.
9 */
10
11#include <linux/fs.h>
12#include <linux/backing-file.h>
13#include <linux/splice.h>
14#include <linux/mm.h>
15
16#include "internal.h"
17
18/**
19 * backing_file_open - open a backing file for kernel internal use
20 * @user_path: path that the user reuqested to open
21 * @flags: open flags
22 * @real_path: path of the backing file
23 * @cred: credentials for open
24 *
25 * Open a backing file for a stackable filesystem (e.g., overlayfs).
26 * @user_path may be on the stackable filesystem and @real_path on the
27 * underlying filesystem. In this case, we want to be able to return the
28 * @user_path of the stackable filesystem. This is done by embedding the
29 * returned file into a container structure that also stores the stacked
30 * file's path, which can be retrieved using backing_file_user_path().
31 */
32struct file *backing_file_open(const struct path *user_path, int flags,
33 const struct path *real_path,
34 const struct cred *cred)
35{
36 struct file *f;
37 int error;
38
39 f = alloc_empty_backing_file(flags, cred);
40 if (IS_ERR(ptr: f))
41 return f;
42
43 path_get(user_path);
44 *backing_file_user_path(f) = *user_path;
45 error = vfs_open(real_path, f);
46 if (error) {
47 fput(f);
48 f = ERR_PTR(error);
49 }
50
51 return f;
52}
53EXPORT_SYMBOL_GPL(backing_file_open);
54
55struct backing_aio {
56 struct kiocb iocb;
57 refcount_t ref;
58 struct kiocb *orig_iocb;
59 /* used for aio completion */
60 void (*end_write)(struct file *);
61 struct work_struct work;
62 long res;
63};
64
65static struct kmem_cache *backing_aio_cachep;
66
67#define BACKING_IOCB_MASK \
68 (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
69
70static rwf_t iocb_to_rw_flags(int flags)
71{
72 return (__force rwf_t)(flags & BACKING_IOCB_MASK);
73}
74
75static void backing_aio_put(struct backing_aio *aio)
76{
77 if (refcount_dec_and_test(r: &aio->ref)) {
78 fput(aio->iocb.ki_filp);
79 kmem_cache_free(s: backing_aio_cachep, objp: aio);
80 }
81}
82
83static void backing_aio_cleanup(struct backing_aio *aio, long res)
84{
85 struct kiocb *iocb = &aio->iocb;
86 struct kiocb *orig_iocb = aio->orig_iocb;
87
88 if (aio->end_write)
89 aio->end_write(orig_iocb->ki_filp);
90
91 orig_iocb->ki_pos = iocb->ki_pos;
92 backing_aio_put(aio);
93}
94
95static void backing_aio_rw_complete(struct kiocb *iocb, long res)
96{
97 struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
98 struct kiocb *orig_iocb = aio->orig_iocb;
99
100 if (iocb->ki_flags & IOCB_WRITE)
101 kiocb_end_write(iocb);
102
103 backing_aio_cleanup(aio, res);
104 orig_iocb->ki_complete(orig_iocb, res);
105}
106
107static void backing_aio_complete_work(struct work_struct *work)
108{
109 struct backing_aio *aio = container_of(work, struct backing_aio, work);
110
111 backing_aio_rw_complete(iocb: &aio->iocb, res: aio->res);
112}
113
114static void backing_aio_queue_completion(struct kiocb *iocb, long res)
115{
116 struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
117
118 /*
119 * Punt to a work queue to serialize updates of mtime/size.
120 */
121 aio->res = res;
122 INIT_WORK(&aio->work, backing_aio_complete_work);
123 queue_work(wq: file_inode(f: aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
124 work: &aio->work);
125}
126
127static int backing_aio_init_wq(struct kiocb *iocb)
128{
129 struct super_block *sb = file_inode(f: iocb->ki_filp)->i_sb;
130
131 if (sb->s_dio_done_wq)
132 return 0;
133
134 return sb_init_dio_done_wq(sb);
135}
136
137
138ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
139 struct kiocb *iocb, int flags,
140 struct backing_file_ctx *ctx)
141{
142 struct backing_aio *aio = NULL;
143 const struct cred *old_cred;
144 ssize_t ret;
145
146 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
147 return -EIO;
148
149 if (!iov_iter_count(i: iter))
150 return 0;
151
152 if (iocb->ki_flags & IOCB_DIRECT &&
153 !(file->f_mode & FMODE_CAN_ODIRECT))
154 return -EINVAL;
155
156 old_cred = override_creds(ctx->cred);
157 if (is_sync_kiocb(kiocb: iocb)) {
158 rwf_t rwf = iocb_to_rw_flags(flags);
159
160 ret = vfs_iter_read(file, iter, ppos: &iocb->ki_pos, flags: rwf);
161 } else {
162 ret = -ENOMEM;
163 aio = kmem_cache_zalloc(k: backing_aio_cachep, GFP_KERNEL);
164 if (!aio)
165 goto out;
166
167 aio->orig_iocb = iocb;
168 kiocb_clone(kiocb: &aio->iocb, kiocb_src: iocb, filp: get_file(f: file));
169 aio->iocb.ki_complete = backing_aio_rw_complete;
170 refcount_set(r: &aio->ref, n: 2);
171 ret = vfs_iocb_iter_read(file, iocb: &aio->iocb, iter);
172 backing_aio_put(aio);
173 if (ret != -EIOCBQUEUED)
174 backing_aio_cleanup(aio, res: ret);
175 }
176out:
177 revert_creds(old_cred);
178
179 if (ctx->accessed)
180 ctx->accessed(ctx->user_file);
181
182 return ret;
183}
184EXPORT_SYMBOL_GPL(backing_file_read_iter);
185
186ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
187 struct kiocb *iocb, int flags,
188 struct backing_file_ctx *ctx)
189{
190 const struct cred *old_cred;
191 ssize_t ret;
192
193 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
194 return -EIO;
195
196 if (!iov_iter_count(i: iter))
197 return 0;
198
199 ret = file_remove_privs(ctx->user_file);
200 if (ret)
201 return ret;
202
203 if (iocb->ki_flags & IOCB_DIRECT &&
204 !(file->f_mode & FMODE_CAN_ODIRECT))
205 return -EINVAL;
206
207 /*
208 * Stacked filesystems don't support deferred completions, don't copy
209 * this property in case it is set by the issuer.
210 */
211 flags &= ~IOCB_DIO_CALLER_COMP;
212
213 old_cred = override_creds(ctx->cred);
214 if (is_sync_kiocb(kiocb: iocb)) {
215 rwf_t rwf = iocb_to_rw_flags(flags);
216
217 ret = vfs_iter_write(file, iter, ppos: &iocb->ki_pos, flags: rwf);
218 if (ctx->end_write)
219 ctx->end_write(ctx->user_file);
220 } else {
221 struct backing_aio *aio;
222
223 ret = backing_aio_init_wq(iocb);
224 if (ret)
225 goto out;
226
227 ret = -ENOMEM;
228 aio = kmem_cache_zalloc(k: backing_aio_cachep, GFP_KERNEL);
229 if (!aio)
230 goto out;
231
232 aio->orig_iocb = iocb;
233 aio->end_write = ctx->end_write;
234 kiocb_clone(kiocb: &aio->iocb, kiocb_src: iocb, filp: get_file(f: file));
235 aio->iocb.ki_flags = flags;
236 aio->iocb.ki_complete = backing_aio_queue_completion;
237 refcount_set(r: &aio->ref, n: 2);
238 ret = vfs_iocb_iter_write(file, iocb: &aio->iocb, iter);
239 backing_aio_put(aio);
240 if (ret != -EIOCBQUEUED)
241 backing_aio_cleanup(aio, res: ret);
242 }
243out:
244 revert_creds(old_cred);
245
246 return ret;
247}
248EXPORT_SYMBOL_GPL(backing_file_write_iter);
249
250ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
251 struct pipe_inode_info *pipe, size_t len,
252 unsigned int flags,
253 struct backing_file_ctx *ctx)
254{
255 const struct cred *old_cred;
256 ssize_t ret;
257
258 if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
259 return -EIO;
260
261 old_cred = override_creds(ctx->cred);
262 ret = vfs_splice_read(in, ppos, pipe, len, flags);
263 revert_creds(old_cred);
264
265 if (ctx->accessed)
266 ctx->accessed(ctx->user_file);
267
268 return ret;
269}
270EXPORT_SYMBOL_GPL(backing_file_splice_read);
271
272ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
273 struct file *out, loff_t *ppos, size_t len,
274 unsigned int flags,
275 struct backing_file_ctx *ctx)
276{
277 const struct cred *old_cred;
278 ssize_t ret;
279
280 if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
281 return -EIO;
282
283 ret = file_remove_privs(ctx->user_file);
284 if (ret)
285 return ret;
286
287 old_cred = override_creds(ctx->cred);
288 file_start_write(file: out);
289 ret = iter_file_splice_write(pipe, out, ppos, len, flags);
290 file_end_write(file: out);
291 revert_creds(old_cred);
292
293 if (ctx->end_write)
294 ctx->end_write(ctx->user_file);
295
296 return ret;
297}
298EXPORT_SYMBOL_GPL(backing_file_splice_write);
299
300int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
301 struct backing_file_ctx *ctx)
302{
303 const struct cred *old_cred;
304 int ret;
305
306 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
307 WARN_ON_ONCE(ctx->user_file != vma->vm_file))
308 return -EIO;
309
310 if (!file->f_op->mmap)
311 return -ENODEV;
312
313 vma_set_file(vma, file);
314
315 old_cred = override_creds(ctx->cred);
316 ret = call_mmap(file: vma->vm_file, vma);
317 revert_creds(old_cred);
318
319 if (ctx->accessed)
320 ctx->accessed(ctx->user_file);
321
322 return ret;
323}
324EXPORT_SYMBOL_GPL(backing_file_mmap);
325
326static int __init backing_aio_init(void)
327{
328 backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN);
329 if (!backing_aio_cachep)
330 return -ENOMEM;
331
332 return 0;
333}
334fs_initcall(backing_aio_init);
335

source code of linux/fs/backing-file.c