fs/notify/dnotify/dnotify.c

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