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 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
  65 static struct kmem_cache *backing_aio_cachep;
  66
  67 #define BACKING_IOCB_MASK \
  68         (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
  69
  70 static rwf_t iocb_to_rw_flags(int flags)
  71 {
  72         return (__force rwf_t)(flags & BACKING_IOCB_MASK);
  73 }
  74
  75 static void backing_aio_put(struct backing_aio *aio)
  76 {
  77         if (refcount_dec_and_test(&aio->ref)) {
  78                 fput(aio->iocb.ki_filp);
  79                 kmem_cache_free(backing_aio_cachep, aio);
  80         }
  81 }
  82
  83 static 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
  95 static 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
 107 static 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(&aio->iocb, aio->res);
 112 }
 113
 114 static 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(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
 124                    &aio->work);
 125 }
 126
 127 static int backing_aio_init_wq(struct kiocb *iocb)
 128 {
 129         struct super_block *sb = file_inode(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
 138 ssize_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(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(iocb)) {
 158                 rwf_t rwf = iocb_to_rw_flags(flags);
 159
 160                 ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
 161         } else {
 162                 ret = -ENOMEM;
 163                 aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 164                 if (!aio)
 165                         goto out;
 166
 167                 aio->orig_iocb = iocb;
 168                 kiocb_clone(&aio->iocb, iocb, get_file(file));
 169                 aio->iocb.ki_complete = backing_aio_rw_complete;
 170                 refcount_set(&aio->ref, 2);
 171                 ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
 172                 backing_aio_put(aio);
 173                 if (ret != -EIOCBQUEUED)
 174                         backing_aio_cleanup(aio, ret);
 175         }
 176 out:
 177         revert_creds(old_cred);
 178
 179         if (ctx->accessed)
 180                 ctx->accessed(ctx->user_file);
 181
 182         return ret;
 183 }
 184 EXPORT_SYMBOL_GPL(backing_file_read_iter);
 185
 186 ssize_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(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(iocb)) {
 215                 rwf_t rwf = iocb_to_rw_flags(flags);
 216
 217                 ret = vfs_iter_write(file, iter, &iocb->ki_pos, 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(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(&aio->iocb, iocb, get_file(file));
 235                 aio->iocb.ki_flags = flags;
 236                 aio->iocb.ki_complete = backing_aio_queue_completion;
 237                 refcount_set(&aio->ref, 2);
 238                 ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
 239                 backing_aio_put(aio);
 240                 if (ret != -EIOCBQUEUED)
 241                         backing_aio_cleanup(aio, ret);
 242         }
 243 out:
 244         revert_creds(old_cred);
 245
 246         return ret;
 247 }
 248 EXPORT_SYMBOL_GPL(backing_file_write_iter);
 249
 250 ssize_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 }
 270 EXPORT_SYMBOL_GPL(backing_file_splice_read);
 271
 272 ssize_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(out);
 289         ret = iter_file_splice_write(pipe, out, ppos, len, flags);
 290         file_end_write(out);
 291         revert_creds(old_cred);
 292
 293         if (ctx->end_write)
 294                 ctx->end_write(ctx->user_file);
 295
 296         return ret;
 297 }
 298 EXPORT_SYMBOL_GPL(backing_file_splice_write);
 299
 300 int 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(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 }
 324 EXPORT_SYMBOL_GPL(backing_file_mmap);
 325
 326 static int __init backing_aio_init(void)
 327 {
 328         backing_aio_cachep = kmem_cache_create("backing_aio",
 329                                                sizeof(struct backing_aio),
 330                                                0, SLAB_HWCACHE_ALIGN, NULL);
 331         if (!backing_aio_cachep)
 332                 return -ENOMEM;
 333
 334         return 0;
 335 }
 336 fs_initcall(backing_aio_init);