fs/notify/fanotify/fanotify.c

   1 #include <linux/fanotify.h>
   2 #include <linux/fdtable.h>
   3 #include <linux/fsnotify_backend.h>
   4 #include <linux/init.h>
   5 #include <linux/jiffies.h>
   6 #include <linux/kernel.h> /* UINT_MAX */
   7 #include <linux/mount.h>
   8 #include <linux/sched.h>
   9 #include <linux/sched/user.h>
  10 #include <linux/types.h>
  11 #include <linux/wait.h>
  12
  13 #include "fanotify.h"
  14
  15 static bool should_merge(struct fsnotify_event *old_fsn,
  16                          struct fsnotify_event *new_fsn)
  17 {
  18         struct fanotify_event_info *old, *new;
  19
  20         pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
  21         old = FANOTIFY_E(old_fsn);
  22         new = FANOTIFY_E(new_fsn);
  23
  24         if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
  25             old->path.mnt == new->path.mnt &&
  26             old->path.dentry == new->path.dentry)
  27                 return true;
  28         return false;
  29 }
  30
  31 /* and the list better be locked by something too! */
  32 static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
  33 {
  34         struct fsnotify_event *test_event;
  35
  36         pr_debug("%s: list=%p event=%p\n", __func__, list, event);
  37
  38 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
  39         /*
  40          * Don't merge a permission event with any other event so that we know
  41          * the event structure we have created in fanotify_handle_event() is the
  42          * one we should check for permission response.
  43          */
  44         if (event->mask & FAN_ALL_PERM_EVENTS)
  45                 return 0;
  46 #endif
  47
  48         list_for_each_entry_reverse(test_event, list, list) {
  49                 if (should_merge(test_event, event)) {
  50                         test_event->mask |= event->mask;
  51                         return 1;
  52                 }
  53         }
  54
  55         return 0;
  56 }
  57
  58 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
  59 static int fanotify_get_response(struct fsnotify_group *group,
  60                                  struct fanotify_perm_event_info *event,
  61                                  struct fsnotify_iter_info *iter_info)
  62 {
  63         int ret;
  64
  65         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  66
  67         wait_event(group->fanotify_data.access_waitq, event->response);
  68
  69         /* userspace responded, convert to something usable */
  70         switch (event->response) {
  71         case FAN_ALLOW:
  72                 ret = 0;
  73                 break;
  74         case FAN_DENY:
  75         default:
  76                 ret = -EPERM;
  77         }
  78         event->response = 0;
  79
  80         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  81                  group, event, ret);
  82
  83         return ret;
  84 }
  85 #endif
  86
  87 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  88                                        struct fsnotify_mark *vfsmnt_mark,
  89                                        u32 event_mask,
  90                                        const void *data, int data_type)
  91 {
  92         __u32 marks_mask, marks_ignored_mask;
  93         const struct path *path = data;
  94
  95         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
  96                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
  97                  event_mask, data, data_type);
  98
  99         /* if we don't have enough info to send an event to userspace say no */
 100         if (data_type != FSNOTIFY_EVENT_PATH)
 101                 return false;
 102
 103         /* sorry, fanotify only gives a damn about files and dirs */
 104         if (!d_is_reg(path->dentry) &&
 105             !d_can_lookup(path->dentry))
 106                 return false;
 107
 108         if (inode_mark && vfsmnt_mark) {
 109                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 110                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 111         } else if (inode_mark) {
 112                 /*
 113                  * if the event is for a child and this inode doesn't care about
 114                  * events on the child, don't send it!
 115                  */
 116                 if ((event_mask & FS_EVENT_ON_CHILD) &&
 117                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 118                         return false;
 119                 marks_mask = inode_mark->mask;
 120                 marks_ignored_mask = inode_mark->ignored_mask;
 121         } else if (vfsmnt_mark) {
 122                 marks_mask = vfsmnt_mark->mask;
 123                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 124         } else {
 125                 BUG();
 126         }
 127
 128         if (d_is_dir(path->dentry) &&
 129             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 130                 return false;
 131
 132         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 133                                  ~marks_ignored_mask)
 134                 return true;
 135
 136         return false;
 137 }
 138
 139 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 140                                                  const struct path *path)
 141 {
 142         struct fanotify_event_info *event;
 143
 144 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 145         if (mask & FAN_ALL_PERM_EVENTS) {
 146                 struct fanotify_perm_event_info *pevent;
 147
 148                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 149                                           GFP_KERNEL);
 150                 if (!pevent)
 151                         return NULL;
 152                 event = &pevent->fae;
 153                 pevent->response = 0;
 154                 goto init;
 155         }
 156 #endif
 157         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 158         if (!event)
 159                 return NULL;
 160 init: __maybe_unused
 161         fsnotify_init_event(&event->fse, inode, mask);
 162         event->tgid = get_pid(task_tgid(current));
 163         if (path) {
 164                 event->path = *path;
 165                 path_get(&event->path);
 166         } else {
 167                 event->path.mnt = NULL;
 168                 event->path.dentry = NULL;
 169         }
 170         return event;
 171 }
 172
 173 static int fanotify_handle_event(struct fsnotify_group *group,
 174                                  struct inode *inode,
 175                                  struct fsnotify_mark *inode_mark,
 176                                  struct fsnotify_mark *fanotify_mark,
 177                                  u32 mask, const void *data, int data_type,
 178                                  const unsigned char *file_name, u32 cookie,
 179                                  struct fsnotify_iter_info *iter_info)
 180 {
 181         int ret = 0;
 182         struct fanotify_event_info *event;
 183         struct fsnotify_event *fsn_event;
 184
 185         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 186         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 187         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 188         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 189         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 190         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 191         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 192         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 193         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 194         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 195
 196         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 197                                         data_type))
 198                 return 0;
 199
 200         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 201                  mask);
 202
 203 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 204         if (mask & FAN_ALL_PERM_EVENTS) {
 205                 /*
 206                  * fsnotify_prepare_user_wait() fails if we race with mark
 207                  * deletion.  Just let the operation pass in that case.
 208                  */
 209                 if (!fsnotify_prepare_user_wait(iter_info))
 210                         return 0;
 211         }
 212 #endif
 213
 214         event = fanotify_alloc_event(inode, mask, data);
 215         ret = -ENOMEM;
 216         if (unlikely(!event))
 217                 goto finish;
 218
 219         fsn_event = &event->fse;
 220         ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
 221         if (ret) {
 222                 /* Permission events shouldn't be merged */
 223                 BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
 224                 /* Our event wasn't used in the end. Free it. */
 225                 fsnotify_destroy_event(group, fsn_event);
 226
 227                 ret = 0;
 228                 goto finish;
 229         }
 230
 231 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 232         if (mask & FAN_ALL_PERM_EVENTS) {
 233                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 234                                             iter_info);
 235                 fsnotify_destroy_event(group, fsn_event);
 236         }
 237 finish:
 238         if (mask & FAN_ALL_PERM_EVENTS)
 239                 fsnotify_finish_user_wait(iter_info);
 240 #else
 241 finish:
 242 #endif
 243         return ret;
 244 }
 245
 246 static void fanotify_free_group_priv(struct fsnotify_group *group)
 247 {
 248         struct user_struct *user;
 249
 250         user = group->fanotify_data.user;
 251         atomic_dec(&user->fanotify_listeners);
 252         free_uid(user);
 253 }
 254
 255 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 256 {
 257         struct fanotify_event_info *event;
 258
 259         event = FANOTIFY_E(fsn_event);
 260         path_put(&event->path);
 261         put_pid(event->tgid);
 262 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 263         if (fsn_event->mask & FAN_ALL_PERM_EVENTS) {
 264                 kmem_cache_free(fanotify_perm_event_cachep,
 265                                 FANOTIFY_PE(fsn_event));
 266                 return;
 267         }
 268 #endif
 269         kmem_cache_free(fanotify_event_cachep, event);
 270 }
 271
 272 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 273 {
 274         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 275 }
 276
 277 const struct fsnotify_ops fanotify_fsnotify_ops = {
 278         .handle_event = fanotify_handle_event,
 279         .free_group_priv = fanotify_free_group_priv,
 280         .free_event = fanotify_free_event,
 281         .free_mark = fanotify_free_mark,
 282 };