1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Directory notifications for Linux. 4 * 5 * Copyright (C) 2000,2001,2002 Stephen Rothwell 6 * 7 * Copyright (C) 2009 Eric Paris <Red Hat Inc> 8 * dnotify was largly rewritten to use the new fsnotify infrastructure 9 */ 10 #include <linux/fs.h> 11 #include <linux/module.h> 12 #include <linux/sched.h> 13 #include <linux/sched/signal.h> 14 #include <linux/dnotify.h> 15 #include <linux/init.h> 16 #include <linux/security.h> 17 #include <linux/spinlock.h> 18 #include <linux/slab.h> 19 #include <linux/fsnotify_backend.h> 20 21 static int dir_notify_enable __read_mostly = 1; 22 #ifdef CONFIG_SYSCTL 23 static struct ctl_table dnotify_sysctls[] = { 24 { 25 .procname = "dir-notify-enable", 26 .data = &dir_notify_enable, 27 .maxlen = sizeof(int), 28 .mode = 0644, 29 .proc_handler = proc_dointvec, 30 }, 31 }; 32 static void __init dnotify_sysctl_init(void) 33 { 34 register_sysctl_init("fs", dnotify_sysctls); 35 } 36 #else 37 #define dnotify_sysctl_init() do { } while (0) 38 #endif 39 40 static struct kmem_cache *dnotify_struct_cache __ro_after_init; 41 static struct kmem_cache *dnotify_mark_cache __ro_after_init; 42 static struct fsnotify_group *dnotify_group __ro_after_init; 43 44 /* 45 * dnotify will attach one of these to each inode (i_fsnotify_marks) which 46 * is being watched by dnotify. If multiple userspace applications are watching 47 * the same directory with dnotify their information is chained in dn 48 */ 49 struct dnotify_mark { 50 struct fsnotify_mark fsn_mark; 51 struct dnotify_struct *dn; 52 }; 53 54 /* 55 * When a process starts or stops watching an inode the set of events which 56 * dnotify cares about for that inode may change. This function runs the 57 * list of everything receiving dnotify events about this directory and calculates 58 * the set of all those events. After it updates what dnotify is interested in 59 * it calls the fsnotify function so it can update the set of all events relevant 60 * to this inode. 61 */ 62 static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark) 63 { 64 __u32 new_mask = 0; 65 struct dnotify_struct *dn; 66 struct dnotify_mark *dn_mark = container_of(fsn_mark, 67 struct dnotify_mark, 68 fsn_mark); 69 70 assert_spin_locked(&fsn_mark->lock); 71 72 for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next) 73 new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT); 74 if (fsn_mark->mask == new_mask) 75 return; 76 fsn_mark->mask = new_mask; 77 78 fsnotify_recalc_mask(fsn_mark->connector); 79 } 80 81 /* 82 * Mains fsnotify call where events are delivered to dnotify. 83 * Find the dnotify mark on the relevant inode, run the list of dnotify structs 84 * on that mark and determine which of them has expressed interest in receiving 85 * events of this type. When found send the correct process and signal and 86 * destroy the dnotify struct if it was not registered to receive multiple 87 * events. 88 */ 89 static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask, 90 struct inode *inode, struct inode *dir, 91 const struct qstr *name, u32 cookie) 92 { 93 struct dnotify_mark *dn_mark; 94 struct dnotify_struct *dn; 95 struct dnotify_struct **prev; 96 struct fown_struct *fown; 97 __u32 test_mask = mask & ~FS_EVENT_ON_CHILD; 98 99 /* not a dir, dnotify doesn't care */ 100 if (!dir && !(mask & FS_ISDIR)) 101 return 0; 102 103 dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark); 104 105 spin_lock(&inode_mark->lock); 106 prev = &dn_mark->dn; 107 while ((dn = *prev) != NULL) { 108 if ((dn->dn_mask & test_mask) == 0) { 109 prev = &dn->dn_next; 110 continue; 111 } 112 fown = file_f_owner(dn->dn_filp); 113 send_sigio(fown, dn->dn_fd, POLL_MSG); 114 if (dn->dn_mask & FS_DN_MULTISHOT) 115 prev = &dn->dn_next; 116 else { 117 *prev = dn->dn_next; 118 kmem_cache_free(dnotify_struct_cache, dn); 119 dnotify_recalc_inode_mask(inode_mark); 120 } 121 } 122 123 spin_unlock(&inode_mark->lock); 124 125 return 0; 126 } 127 128 static void dnotify_free_mark(struct fsnotify_mark *fsn_mark) 129 { 130 struct dnotify_mark *dn_mark = container_of(fsn_mark, 131 struct dnotify_mark, 132 fsn_mark); 133 134 BUG_ON(dn_mark->dn); 135 136 kmem_cache_free(dnotify_mark_cache, dn_mark); 137 } 138 139 static const struct fsnotify_ops dnotify_fsnotify_ops = { 140 .handle_inode_event = dnotify_handle_event, 141 .free_mark = dnotify_free_mark, 142 }; 143 144 /* 145 * Called every time a file is closed. Looks first for a dnotify mark on the 146 * inode. If one is found run all of the ->dn structures attached to that 147 * mark for one relevant to this process closing the file and remove that 148 * dnotify_struct. If that was the last dnotify_struct also remove the 149 * fsnotify_mark. 150 */ 151 void dnotify_flush(struct file *filp, fl_owner_t id) 152 { 153 struct fsnotify_mark *fsn_mark; 154 struct dnotify_mark *dn_mark; 155 struct dnotify_struct *dn; 156 struct dnotify_struct **prev; 157 struct inode *inode; 158 bool free = false; 159 160 inode = file_inode(filp); 161 if (!S_ISDIR(inode->i_mode)) 162 return; 163 164 fsn_mark = fsnotify_find_inode_mark(inode, dnotify_group); 165 if (!fsn_mark) 166 return; 167 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 168 169 fsnotify_group_lock(dnotify_group); 170 171 spin_lock(&fsn_mark->lock); 172 prev = &dn_mark->dn; 173 while ((dn = *prev) != NULL) { 174 if ((dn->dn_owner == id) && (dn->dn_filp == filp)) { 175 *prev = dn->dn_next; 176 kmem_cache_free(dnotify_struct_cache, dn); 177 dnotify_recalc_inode_mask(fsn_mark); 178 break; 179 } 180 prev = &dn->dn_next; 181 } 182 183 spin_unlock(&fsn_mark->lock); 184 185 /* nothing else could have found us thanks to the dnotify_groups 186 mark_mutex */ 187 if (dn_mark->dn == NULL) { 188 fsnotify_detach_mark(fsn_mark); 189 free = true; 190 } 191 192 fsnotify_group_unlock(dnotify_group); 193 194 if (free) 195 fsnotify_free_mark(fsn_mark); 196 fsnotify_put_mark(fsn_mark); 197 } 198 199 /* this conversion is done only at watch creation */ 200 static __u32 convert_arg(unsigned int arg) 201 { 202 __u32 new_mask = FS_EVENT_ON_CHILD; 203 204 if (arg & DN_MULTISHOT) 205 new_mask |= FS_DN_MULTISHOT; 206 if (arg & DN_DELETE) 207 new_mask |= (FS_DELETE | FS_MOVED_FROM); 208 if (arg & DN_MODIFY) 209 new_mask |= FS_MODIFY; 210 if (arg & DN_ACCESS) 211 new_mask |= FS_ACCESS; 212 if (arg & DN_ATTRIB) 213 new_mask |= FS_ATTRIB; 214 if (arg & DN_RENAME) 215 new_mask |= FS_RENAME; 216 if (arg & DN_CREATE) 217 new_mask |= (FS_CREATE | FS_MOVED_TO); 218 219 return new_mask; 220 } 221 222 /* 223 * If multiple processes watch the same inode with dnotify there is only one 224 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct 225 * onto that mark. This function either attaches the new dnotify_struct onto 226 * that list, or it |= the mask onto an existing dnofiy_struct. 227 */ 228 static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark, 229 fl_owner_t id, int fd, struct file *filp, __u32 mask) 230 { 231 struct dnotify_struct *odn; 232 233 odn = dn_mark->dn; 234 while (odn != NULL) { 235 /* adding more events to existing dnofiy_struct? */ 236 if ((odn->dn_owner == id) && (odn->dn_filp == filp)) { 237 odn->dn_fd = fd; 238 odn->dn_mask |= mask; 239 return -EEXIST; 240 } 241 odn = odn->dn_next; 242 } 243 244 dn->dn_mask = mask; 245 dn->dn_fd = fd; 246 dn->dn_filp = filp; 247 dn->dn_owner = id; 248 dn->dn_next = dn_mark->dn; 249 dn_mark->dn = dn; 250 251 return 0; 252 } 253 254 /* 255 * When a process calls fcntl to attach a dnotify watch to a directory it ends 256 * up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be 257 * attached to the fsnotify_mark. 258 */ 259 int fcntl_dirnotify(int fd, struct file *filp, unsigned int arg) 260 { 261 struct dnotify_mark *new_dn_mark, *dn_mark; 262 struct fsnotify_mark *new_fsn_mark, *fsn_mark; 263 struct dnotify_struct *dn; 264 struct inode *inode; 265 fl_owner_t id = current->files; 266 struct file *f = NULL; 267 int destroy = 0, error = 0; 268 __u32 mask; 269 270 /* we use these to tell if we need to kfree */ 271 new_fsn_mark = NULL; 272 dn = NULL; 273 274 if (!dir_notify_enable) { 275 error = -EINVAL; 276 goto out_err; 277 } 278 279 /* a 0 mask means we are explicitly removing the watch */ 280 if ((arg & ~DN_MULTISHOT) == 0) { 281 dnotify_flush(filp, id); 282 error = 0; 283 goto out_err; 284 } 285 286 /* dnotify only works on directories */ 287 inode = file_inode(filp); 288 if (!S_ISDIR(inode->i_mode)) { 289 error = -ENOTDIR; 290 goto out_err; 291 } 292 293 /* 294 * convert the userspace DN_* "arg" to the internal FS_* 295 * defined in fsnotify 296 */ 297 mask = convert_arg(arg); 298 299 error = security_path_notify(&filp->f_path, mask, 300 FSNOTIFY_OBJ_TYPE_INODE); 301 if (error) 302 goto out_err; 303 304 /* expect most fcntl to add new rather than augment old */ 305 dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL); 306 if (!dn) { 307 error = -ENOMEM; 308 goto out_err; 309 } 310 311 /* new fsnotify mark, we expect most fcntl calls to add a new mark */ 312 new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL); 313 if (!new_dn_mark) { 314 error = -ENOMEM; 315 goto out_err; 316 } 317 318 error = file_f_owner_allocate(filp); 319 if (error) 320 goto out_err; 321 322 /* set up the new_fsn_mark and new_dn_mark */ 323 new_fsn_mark = &new_dn_mark->fsn_mark; 324 fsnotify_init_mark(new_fsn_mark, dnotify_group); 325 new_fsn_mark->mask = mask; 326 new_dn_mark->dn = NULL; 327 328 /* this is needed to prevent the fcntl/close race described below */ 329 fsnotify_group_lock(dnotify_group); 330 331 /* add the new_fsn_mark or find an old one. */ 332 fsn_mark = fsnotify_find_inode_mark(inode, dnotify_group); 333 if (fsn_mark) { 334 dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark); 335 spin_lock(&fsn_mark->lock); 336 } else { 337 error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0); 338 if (error) { 339 fsnotify_group_unlock(dnotify_group); 340 goto out_err; 341 } 342 spin_lock(&new_fsn_mark->lock); 343 fsn_mark = new_fsn_mark; 344 dn_mark = new_dn_mark; 345 /* we used new_fsn_mark, so don't free it */ 346 new_fsn_mark = NULL; 347 } 348 349 f = fget_raw(fd); 350 351 /* if (f != filp) means that we lost a race and another task/thread 352 * actually closed the fd we are still playing with before we grabbed 353 * the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the 354 * fd is the only time we clean up the marks we need to get our mark 355 * off the list. */ 356 if (f != filp) { 357 /* if we added ourselves, shoot ourselves, it's possible that 358 * the flush actually did shoot this fsn_mark. That's fine too 359 * since multiple calls to destroy_mark is perfectly safe, if 360 * we found a dn_mark already attached to the inode, just sod 361 * off silently as the flush at close time dealt with it. 362 */ 363 if (dn_mark == new_dn_mark) 364 destroy = 1; 365 error = 0; 366 goto out; 367 } 368 369 __f_setown(filp, task_pid(current), PIDTYPE_TGID, 0); 370 371 error = attach_dn(dn, dn_mark, id, fd, filp, mask); 372 /* !error means that we attached the dn to the dn_mark, so don't free it */ 373 if (!error) 374 dn = NULL; 375 /* -EEXIST means that we didn't add this new dn and used an old one. 376 * that isn't an error (and the unused dn should be freed) */ 377 else if (error == -EEXIST) 378 error = 0; 379 380 dnotify_recalc_inode_mask(fsn_mark); 381 out: 382 spin_unlock(&fsn_mark->lock); 383 384 if (destroy) 385 fsnotify_detach_mark(fsn_mark); 386 fsnotify_group_unlock(dnotify_group); 387 if (destroy) 388 fsnotify_free_mark(fsn_mark); 389 fsnotify_put_mark(fsn_mark); 390 out_err: 391 if (new_fsn_mark) 392 fsnotify_put_mark(new_fsn_mark); 393 if (dn) 394 kmem_cache_free(dnotify_struct_cache, dn); 395 if (f) 396 fput(f); 397 return error; 398 } 399 400 static int __init dnotify_init(void) 401 { 402 dnotify_struct_cache = KMEM_CACHE(dnotify_struct, 403 SLAB_PANIC|SLAB_ACCOUNT); 404 dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT); 405 406 dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops, 0); 407 if (IS_ERR(dnotify_group)) 408 panic("unable to allocate fsnotify group for dnotify\n"); 409 dnotify_sysctl_init(); 410 return 0; 411 } 412 413 module_init(dnotify_init) 414