fs/backing-file.c

   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  */
  32 struct 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(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 }
  53 EXPORT_SYMBOL_GPL(backing_file_open);
  54
  55 struct file *backing_tmpfile_open(const struct path *user_path, int flags,
  56                                   const struct path *real_parentpath,
  57                                   umode_t mode, const struct cred *cred)
  58 {
  59         struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt);
  60         struct file *f;
  61         int error;
  62
  63         f = alloc_empty_backing_file(flags, cred);
  64         if (IS_ERR(f))
  65                 return f;
  66
  67         path_get(user_path);
  68         *backing_file_user_path(f) = *user_path;
  69         error = vfs_tmpfile(real_idmap, real_parentpath, f, mode);
  70         if (error) {
  71                 fput(f);
  72                 f = ERR_PTR(error);
  73         }
  74         return f;
  75 }
  76 EXPORT_SYMBOL(backing_tmpfile_open);
  77
  78 struct backing_aio {
  79         struct kiocb iocb;
  80         refcount_t ref;
  81         struct kiocb *orig_iocb;
  82         /* used for aio completion */
  83         void (*end_write)(struct file *);
  84         struct work_struct work;
  85         long res;
  86 };
  87
  88 static struct kmem_cache *backing_aio_cachep;
  89
  90 #define BACKING_IOCB_MASK \
  91         (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
  92
  93 static rwf_t iocb_to_rw_flags(int flags)
  94 {
  95         return (__force rwf_t)(flags & BACKING_IOCB_MASK);
  96 }
  97
  98 static void backing_aio_put(struct backing_aio *aio)
  99 {
 100         if (refcount_dec_and_test(&aio->ref)) {
 101                 fput(aio->iocb.ki_filp);
 102                 kmem_cache_free(backing_aio_cachep, aio);
 103         }
 104 }
 105
 106 static void backing_aio_cleanup(struct backing_aio *aio, long res)
 107 {
 108         struct kiocb *iocb = &aio->iocb;
 109         struct kiocb *orig_iocb = aio->orig_iocb;
 110
 111         if (aio->end_write)
 112                 aio->end_write(orig_iocb->ki_filp);
 113
 114         orig_iocb->ki_pos = iocb->ki_pos;
 115         backing_aio_put(aio);
 116 }
 117
 118 static void backing_aio_rw_complete(struct kiocb *iocb, long res)
 119 {
 120         struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
 121         struct kiocb *orig_iocb = aio->orig_iocb;
 122
 123         if (iocb->ki_flags & IOCB_WRITE)
 124                 kiocb_end_write(iocb);
 125
 126         backing_aio_cleanup(aio, res);
 127         orig_iocb->ki_complete(orig_iocb, res);
 128 }
 129
 130 static void backing_aio_complete_work(struct work_struct *work)
 131 {
 132         struct backing_aio *aio = container_of(work, struct backing_aio, work);
 133
 134         backing_aio_rw_complete(&aio->iocb, aio->res);
 135 }
 136
 137 static void backing_aio_queue_completion(struct kiocb *iocb, long res)
 138 {
 139         struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
 140
 141         /*
 142          * Punt to a work queue to serialize updates of mtime/size.
 143          */
 144         aio->res = res;
 145         INIT_WORK(&aio->work, backing_aio_complete_work);
 146         queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
 147                    &aio->work);
 148 }
 149
 150 static int backing_aio_init_wq(struct kiocb *iocb)
 151 {
 152         struct super_block *sb = file_inode(iocb->ki_filp)->i_sb;
 153
 154         if (sb->s_dio_done_wq)
 155                 return 0;
 156
 157         return sb_init_dio_done_wq(sb);
 158 }
 159
 160
 161 ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 162                                struct kiocb *iocb, int flags,
 163                                struct backing_file_ctx *ctx)
 164 {
 165         struct backing_aio *aio = NULL;
 166         const struct cred *old_cred;
 167         ssize_t ret;
 168
 169         if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
 170                 return -EIO;
 171
 172         if (!iov_iter_count(iter))
 173                 return 0;
 174
 175         if (iocb->ki_flags & IOCB_DIRECT &&
 176             !(file->f_mode & FMODE_CAN_ODIRECT))
 177                 return -EINVAL;
 178
 179         old_cred = override_creds(ctx->cred);
 180         if (is_sync_kiocb(iocb)) {
 181                 rwf_t rwf = iocb_to_rw_flags(flags);
 182
 183                 ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
 184         } else {
 185                 ret = -ENOMEM;
 186                 aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 187                 if (!aio)
 188                         goto out;
 189
 190                 aio->orig_iocb = iocb;
 191                 kiocb_clone(&aio->iocb, iocb, get_file(file));
 192                 aio->iocb.ki_complete = backing_aio_rw_complete;
 193                 refcount_set(&aio->ref, 2);
 194                 ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
 195                 backing_aio_put(aio);
 196                 if (ret != -EIOCBQUEUED)
 197                         backing_aio_cleanup(aio, ret);
 198         }
 199 out:
 200         revert_creds(old_cred);
 201
 202         if (ctx->accessed)
 203                 ctx->accessed(ctx->user_file);
 204
 205         return ret;
 206 }
 207 EXPORT_SYMBOL_GPL(backing_file_read_iter);
 208
 209 ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 210                                 struct kiocb *iocb, int flags,
 211                                 struct backing_file_ctx *ctx)
 212 {
 213         const struct cred *old_cred;
 214         ssize_t ret;
 215
 216         if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
 217                 return -EIO;
 218
 219         if (!iov_iter_count(iter))
 220                 return 0;
 221
 222         ret = file_remove_privs(ctx->user_file);
 223         if (ret)
 224                 return ret;
 225
 226         if (iocb->ki_flags & IOCB_DIRECT &&
 227             !(file->f_mode & FMODE_CAN_ODIRECT))
 228                 return -EINVAL;
 229
 230         /*
 231          * Stacked filesystems don't support deferred completions, don't copy
 232          * this property in case it is set by the issuer.
 233          */
 234         flags &= ~IOCB_DIO_CALLER_COMP;
 235
 236         old_cred = override_creds(ctx->cred);
 237         if (is_sync_kiocb(iocb)) {
 238                 rwf_t rwf = iocb_to_rw_flags(flags);
 239
 240                 ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
 241                 if (ctx->end_write)
 242                         ctx->end_write(ctx->user_file);
 243         } else {
 244                 struct backing_aio *aio;
 245
 246                 ret = backing_aio_init_wq(iocb);
 247                 if (ret)
 248                         goto out;
 249
 250                 ret = -ENOMEM;
 251                 aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 252                 if (!aio)
 253                         goto out;
 254
 255                 aio->orig_iocb = iocb;
 256                 aio->end_write = ctx->end_write;
 257                 kiocb_clone(&aio->iocb, iocb, get_file(file));
 258                 aio->iocb.ki_flags = flags;
 259                 aio->iocb.ki_complete = backing_aio_queue_completion;
 260                 refcount_set(&aio->ref, 2);
 261                 ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
 262                 backing_aio_put(aio);
 263                 if (ret != -EIOCBQUEUED)
 264                         backing_aio_cleanup(aio, ret);
 265         }
 266 out:
 267         revert_creds(old_cred);
 268
 269         return ret;
 270 }
 271 EXPORT_SYMBOL_GPL(backing_file_write_iter);
 272
 273 ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
 274                                  struct pipe_inode_info *pipe, size_t len,
 275                                  unsigned int flags,
 276                                  struct backing_file_ctx *ctx)
 277 {
 278         const struct cred *old_cred;
 279         ssize_t ret;
 280
 281         if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
 282                 return -EIO;
 283
 284         old_cred = override_creds(ctx->cred);
 285         ret = vfs_splice_read(in, ppos, pipe, len, flags);
 286         revert_creds(old_cred);
 287
 288         if (ctx->accessed)
 289                 ctx->accessed(ctx->user_file);
 290
 291         return ret;
 292 }
 293 EXPORT_SYMBOL_GPL(backing_file_splice_read);
 294
 295 ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
 296                                   struct file *out, loff_t *ppos, size_t len,
 297                                   unsigned int flags,
 298                                   struct backing_file_ctx *ctx)
 299 {
 300         const struct cred *old_cred;
 301         ssize_t ret;
 302
 303         if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
 304                 return -EIO;
 305
 306         ret = file_remove_privs(ctx->user_file);
 307         if (ret)
 308                 return ret;
 309
 310         old_cred = override_creds(ctx->cred);
 311         file_start_write(out);
 312         ret = iter_file_splice_write(pipe, out, ppos, len, flags);
 313         file_end_write(out);
 314         revert_creds(old_cred);
 315
 316         if (ctx->end_write)
 317                 ctx->end_write(ctx->user_file);
 318
 319         return ret;
 320 }
 321 EXPORT_SYMBOL_GPL(backing_file_splice_write);
 322
 323 int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
 324                       struct backing_file_ctx *ctx)
 325 {
 326         const struct cred *old_cred;
 327         int ret;
 328
 329         if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
 330             WARN_ON_ONCE(ctx->user_file != vma->vm_file))
 331                 return -EIO;
 332
 333         if (!file->f_op->mmap)
 334                 return -ENODEV;
 335
 336         vma_set_file(vma, file);
 337
 338         old_cred = override_creds(ctx->cred);
 339         ret = call_mmap(vma->vm_file, vma);
 340         revert_creds(old_cred);
 341
 342         if (ctx->accessed)
 343                 ctx->accessed(ctx->user_file);
 344
 345         return ret;
 346 }
 347 EXPORT_SYMBOL_GPL(backing_file_mmap);
 348
 349 static int __init backing_aio_init(void)
 350 {
 351         backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN);
 352         if (!backing_aio_cachep)
 353                 return -ENOMEM;
 354
 355         return 0;
 356 }
 357 fs_initcall(backing_aio_init);