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_file_modified(struct file *file) 22 { 23 struct inode *inode = file_inode(file); 24 25 fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE); 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 .user_file = file, 38 .accessed = fuse_file_accessed, 39 }; 40 41 42 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__, 43 backing_file, iocb->ki_pos, count); 44 45 if (!count) 46 return 0; 47 48 ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags, 49 &ctx); 50 51 return ret; 52 } 53 54 ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, 55 struct iov_iter *iter) 56 { 57 struct file *file = iocb->ki_filp; 58 struct inode *inode = file_inode(file); 59 struct fuse_file *ff = file->private_data; 60 struct file *backing_file = fuse_file_passthrough(ff); 61 size_t count = iov_iter_count(iter); 62 ssize_t ret; 63 struct backing_file_ctx ctx = { 64 .cred = ff->cred, 65 .user_file = file, 66 .end_write = fuse_file_modified, 67 }; 68 69 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__, 70 backing_file, iocb->ki_pos, count); 71 72 if (!count) 73 return 0; 74 75 inode_lock(inode); 76 ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags, 77 &ctx); 78 inode_unlock(inode); 79 80 return ret; 81 } 82 83 ssize_t fuse_passthrough_splice_read(struct file *in, loff_t *ppos, 84 struct pipe_inode_info *pipe, 85 size_t len, unsigned int flags) 86 { 87 struct fuse_file *ff = in->private_data; 88 struct file *backing_file = fuse_file_passthrough(ff); 89 struct backing_file_ctx ctx = { 90 .cred = ff->cred, 91 .user_file = in, 92 .accessed = fuse_file_accessed, 93 }; 94 95 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__, 96 backing_file, ppos ? *ppos : 0, len, flags); 97 98 return backing_file_splice_read(backing_file, ppos, pipe, len, flags, 99 &ctx); 100 } 101 102 ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe, 103 struct file *out, loff_t *ppos, 104 size_t len, unsigned int flags) 105 { 106 struct fuse_file *ff = out->private_data; 107 struct file *backing_file = fuse_file_passthrough(ff); 108 struct inode *inode = file_inode(out); 109 ssize_t ret; 110 struct backing_file_ctx ctx = { 111 .cred = ff->cred, 112 .user_file = out, 113 .end_write = fuse_file_modified, 114 }; 115 116 pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__, 117 backing_file, ppos ? *ppos : 0, len, flags); 118 119 inode_lock(inode); 120 ret = backing_file_splice_write(pipe, backing_file, ppos, len, flags, 121 &ctx); 122 inode_unlock(inode); 123 124 return ret; 125 } 126 127 ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma) 128 { 129 struct fuse_file *ff = file->private_data; 130 struct file *backing_file = fuse_file_passthrough(ff); 131 struct backing_file_ctx ctx = { 132 .cred = ff->cred, 133 .user_file = file, 134 .accessed = fuse_file_accessed, 135 }; 136 137 pr_debug("%s: backing_file=0x%p, start=%lu, end=%lu\n", __func__, 138 backing_file, vma->vm_start, vma->vm_end); 139 140 return backing_file_mmap(backing_file, vma, &ctx); 141 } 142 143 struct fuse_backing *fuse_backing_get(struct fuse_backing *fb) 144 { 145 if (fb && refcount_inc_not_zero(&fb->count)) 146 return fb; 147 return NULL; 148 } 149 150 static void fuse_backing_free(struct fuse_backing *fb) 151 { 152 pr_debug("%s: fb=0x%p\n", __func__, fb); 153 154 if (fb->file) 155 fput(fb->file); 156 put_cred(fb->cred); 157 kfree_rcu(fb, rcu); 158 } 159 160 void fuse_backing_put(struct fuse_backing *fb) 161 { 162 if (fb && refcount_dec_and_test(&fb->count)) 163 fuse_backing_free(fb); 164 } 165 166 void fuse_backing_files_init(struct fuse_conn *fc) 167 { 168 idr_init(&fc->backing_files_map); 169 } 170 171 static int fuse_backing_id_alloc(struct fuse_conn *fc, struct fuse_backing *fb) 172 { 173 int id; 174 175 idr_preload(GFP_KERNEL); 176 spin_lock(&fc->lock); 177 /* FIXME: xarray might be space inefficient */ 178 id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC); 179 spin_unlock(&fc->lock); 180 idr_preload_end(); 181 182 WARN_ON_ONCE(id == 0); 183 return id; 184 } 185 186 static struct fuse_backing *fuse_backing_id_remove(struct fuse_conn *fc, 187 int id) 188 { 189 struct fuse_backing *fb; 190 191 spin_lock(&fc->lock); 192 fb = idr_remove(&fc->backing_files_map, id); 193 spin_unlock(&fc->lock); 194 195 return fb; 196 } 197 198 static int fuse_backing_id_free(int id, void *p, void *data) 199 { 200 struct fuse_backing *fb = p; 201 202 WARN_ON_ONCE(refcount_read(&fb->count) != 1); 203 fuse_backing_free(fb); 204 return 0; 205 } 206 207 void fuse_backing_files_free(struct fuse_conn *fc) 208 { 209 idr_for_each(&fc->backing_files_map, fuse_backing_id_free, NULL); 210 idr_destroy(&fc->backing_files_map); 211 } 212 213 int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map) 214 { 215 struct file *file; 216 struct super_block *backing_sb; 217 struct fuse_backing *fb = NULL; 218 int res; 219 220 pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags); 221 222 /* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */ 223 res = -EPERM; 224 if (!fc->passthrough || !capable(CAP_SYS_ADMIN)) 225 goto out; 226 227 res = -EINVAL; 228 if (map->flags) 229 goto out; 230 231 file = fget(map->fd); 232 res = -EBADF; 233 if (!file) 234 goto out; 235 236 res = -EOPNOTSUPP; 237 if (!file->f_op->read_iter || !file->f_op->write_iter) 238 goto out_fput; 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 } 356