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/types.h>
  10 #include <linux/wait.h>
  11
  12 static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
  13 {
  14         pr_debug("%s: old=%p new=%p\n", __func__, old, new);
  15
  16         if (old->to_tell == new->to_tell &&
  17             old->data_type == new->data_type &&
  18             old->tgid == new->tgid) {
  19                 switch (old->data_type) {
  20                 case (FSNOTIFY_EVENT_PATH):
  21                         if ((old->path.mnt == new->path.mnt) &&
  22                             (old->path.dentry == new->path.dentry))
  23                                 return true;
  24                 case (FSNOTIFY_EVENT_NONE):
  25                         return true;
  26                 default:
  27                         BUG();
  28                 };
  29         }
  30         return false;
  31 }
  32
  33 /* and the list better be locked by something too! */
  34 static struct fsnotify_event *fanotify_merge(struct list_head *list,
  35                                              struct fsnotify_event *event)
  36 {
  37         struct fsnotify_event_holder *test_holder;
  38         struct fsnotify_event *test_event = NULL;
  39         struct fsnotify_event *new_event;
  40
  41         pr_debug("%s: list=%p event=%p\n", __func__, list, event);
  42
  43
  44         list_for_each_entry_reverse(test_holder, list, event_list) {
  45                 if (should_merge(test_holder->event, event)) {
  46                         test_event = test_holder->event;
  47                         break;
  48                 }
  49         }
  50
  51         if (!test_event)
  52                 return NULL;
  53
  54         fsnotify_get_event(test_event);
  55
  56         /* if they are exactly the same we are done */
  57         if (test_event->mask == event->mask)
  58                 return test_event;
  59
  60         /*
  61          * if the refcnt == 2 this is the only queue
  62          * for this event and so we can update the mask
  63          * in place.
  64          */
  65         if (atomic_read(&test_event->refcnt) == 2) {
  66                 test_event->mask |= event->mask;
  67                 return test_event;
  68         }
  69
  70         new_event = fsnotify_clone_event(test_event);
  71
  72         /* done with test_event */
  73         fsnotify_put_event(test_event);
  74
  75         /* couldn't allocate memory, merge was not possible */
  76         if (unlikely(!new_event))
  77                 return ERR_PTR(-ENOMEM);
  78
  79         /* build new event and replace it on the list */
  80         new_event->mask = (test_event->mask | event->mask);
  81         fsnotify_replace_event(test_holder, new_event);
  82
  83         /* we hold a reference on new_event from clone_event */
  84         return new_event;
  85 }
  86
  87 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
  88 static int fanotify_get_response_from_access(struct fsnotify_group *group,
  89                                              struct fsnotify_event *event)
  90 {
  91         int ret;
  92
  93         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  94
  95         wait_event(group->fanotify_data.access_waitq, event->response ||
  96                                 atomic_read(&group->fanotify_data.bypass_perm));
  97
  98         if (!event->response) /* bypass_perm set */
  99                 return 0;
 100
 101         /* userspace responded, convert to something usable */
 102         spin_lock(&event->lock);
 103         switch (event->response) {
 104         case FAN_ALLOW:
 105                 ret = 0;
 106                 break;
 107         case FAN_DENY:
 108         default:
 109                 ret = -EPERM;
 110         }
 111         event->response = 0;
 112         spin_unlock(&event->lock);
 113
 114         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
 115                  group, event, ret);
 116
 117         return ret;
 118 }
 119 #endif
 120
 121 static int fanotify_handle_event(struct fsnotify_group *group,
 122                                  struct fsnotify_mark *inode_mark,
 123                                  struct fsnotify_mark *fanotify_mark,
 124                                  struct fsnotify_event *event)
 125 {
 126         int ret = 0;
 127         struct fsnotify_event *notify_event = NULL;
 128
 129         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 130         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 131         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 132         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 133         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 134         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 135         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 136         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 137         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 138         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 139
 140         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 141
 142         notify_event = fsnotify_add_notify_event(group, event, NULL, fanotify_merge);
 143         if (IS_ERR(notify_event))
 144                 return PTR_ERR(notify_event);
 145
 146 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 147         if (event->mask & FAN_ALL_PERM_EVENTS) {
 148                 /* if we merged we need to wait on the new event */
 149                 if (notify_event)
 150                         event = notify_event;
 151                 ret = fanotify_get_response_from_access(group, event);
 152         }
 153 #endif
 154
 155         if (notify_event)
 156                 fsnotify_put_event(notify_event);
 157
 158         return ret;
 159 }
 160
 161 static bool fanotify_should_send_event(struct fsnotify_group *group,
 162                                        struct inode *to_tell,
 163                                        struct fsnotify_mark *inode_mark,
 164                                        struct fsnotify_mark *vfsmnt_mark,
 165                                        __u32 event_mask, void *data, int data_type)
 166 {
 167         __u32 marks_mask, marks_ignored_mask;
 168         struct path *path = data;
 169
 170         pr_debug("%s: group=%p to_tell=%p inode_mark=%p vfsmnt_mark=%p "
 171                  "mask=%x data=%p data_type=%d\n", __func__, group, to_tell,
 172                  inode_mark, vfsmnt_mark, event_mask, data, data_type);
 173
 174         /* if we don't have enough info to send an event to userspace say no */
 175         if (data_type != FSNOTIFY_EVENT_PATH)
 176                 return false;
 177
 178         /* sorry, fanotify only gives a damn about files and dirs */
 179         if (!S_ISREG(path->dentry->d_inode->i_mode) &&
 180             !S_ISDIR(path->dentry->d_inode->i_mode))
 181                 return false;
 182
 183         if (inode_mark && vfsmnt_mark) {
 184                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 185                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 186         } else if (inode_mark) {
 187                 marks_mask = inode_mark->mask;
 188                 marks_ignored_mask = inode_mark->ignored_mask;
 189         } else if (vfsmnt_mark) {
 190                 marks_mask = vfsmnt_mark->mask;
 191                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 192         } else {
 193                 BUG();
 194         }
 195
 196         if (S_ISDIR(path->dentry->d_inode->i_mode) &&
 197             (marks_ignored_mask & FS_ISDIR))
 198                 return false;
 199
 200         /*
 201          * if the event is for a child and this inode doesn't care about
 202          * events on the child, don't send it!
 203          */
 204         if ((event_mask & FS_EVENT_ON_CHILD) &&
 205             !(marks_mask & FS_EVENT_ON_CHILD))
 206                 return false;
 207
 208         /*
 209          * It might seem logical to check:
 210          * if (event_mask & marks_mask & ~marks_ignored_mask)
 211          *      return true;
 212          * but we we know this was true from the caller so just return true.
 213          */
 214         return true;
 215 }
 216
 217 static void fanotify_free_group_priv(struct fsnotify_group *group)
 218 {
 219         struct user_struct *user;
 220
 221         user = group->fanotify_data.user;
 222         atomic_dec(&user->fanotify_listeners);
 223         free_uid(user);
 224 }
 225
 226 const struct fsnotify_ops fanotify_fsnotify_ops = {
 227         .handle_event = fanotify_handle_event,
 228         .should_send_event = fanotify_should_send_event,
 229         .free_group_priv = fanotify_free_group_priv,
 230         .free_event_priv = NULL,
 231         .freeing_mark = NULL,
 232 };