fs/fuse/passthrough.c

   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_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
  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
  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
  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
 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
 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
 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
 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
 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
 170 void fuse_backing_files_init(struct fuse_conn *fc)
 171 {
 172         idr_init(&fc->backing_files_map);
 173 }
 174
 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
 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
 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
 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
 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         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 }