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 {
  62         int ret;
  63
  64         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  65
  66         wait_event(group->fanotify_data.access_waitq, event->response);
  67
  68         /* userspace responded, convert to something usable */
  69         switch (event->response) {
  70         case FAN_ALLOW:
  71                 ret = 0;
  72                 break;
  73         case FAN_DENY:
  74         default:
  75                 ret = -EPERM;
  76         }
  77         event->response = 0;
  78
  79         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  80                  group, event, ret);
  81
  82         return ret;
  83 }
  84 #endif
  85
  86 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  87                                        struct fsnotify_mark *vfsmnt_mark,
  88                                        u32 event_mask,
  89                                        const void *data, int data_type)
  90 {
  91         __u32 marks_mask, marks_ignored_mask;
  92         const struct path *path = data;
  93
  94         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
  95                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
  96                  event_mask, data, data_type);
  97
  98         /* if we don't have enough info to send an event to userspace say no */
  99         if (data_type != FSNOTIFY_EVENT_PATH)
 100                 return false;
 101
 102         /* sorry, fanotify only gives a damn about files and dirs */
 103         if (!d_is_reg(path->dentry) &&
 104             !d_can_lookup(path->dentry))
 105                 return false;
 106
 107         if (inode_mark && vfsmnt_mark) {
 108                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 109                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 110         } else if (inode_mark) {
 111                 /*
 112                  * if the event is for a child and this inode doesn't care about
 113                  * events on the child, don't send it!
 114                  */
 115                 if ((event_mask & FS_EVENT_ON_CHILD) &&
 116                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 117                         return false;
 118                 marks_mask = inode_mark->mask;
 119                 marks_ignored_mask = inode_mark->ignored_mask;
 120         } else if (vfsmnt_mark) {
 121                 marks_mask = vfsmnt_mark->mask;
 122                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 123         } else {
 124                 BUG();
 125         }
 126
 127         if (d_is_dir(path->dentry) &&
 128             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 129                 return false;
 130
 131         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 132                                  ~marks_ignored_mask)
 133                 return true;
 134
 135         return false;
 136 }
 137
 138 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 139                                                  const struct path *path)
 140 {
 141         struct fanotify_event_info *event;
 142
 143 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 144         if (mask & FAN_ALL_PERM_EVENTS) {
 145                 struct fanotify_perm_event_info *pevent;
 146
 147                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 148                                           GFP_KERNEL);
 149                 if (!pevent)
 150                         return NULL;
 151                 event = &pevent->fae;
 152                 pevent->response = 0;
 153                 goto init;
 154         }
 155 #endif
 156         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 157         if (!event)
 158                 return NULL;
 159 init: __maybe_unused
 160         fsnotify_init_event(&event->fse, inode, mask);
 161         event->tgid = get_pid(task_tgid(current));
 162         if (path) {
 163                 event->path = *path;
 164                 path_get(&event->path);
 165         } else {
 166                 event->path.mnt = NULL;
 167                 event->path.dentry = NULL;
 168         }
 169         return event;
 170 }
 171
 172 static int fanotify_handle_event(struct fsnotify_group *group,
 173                                  struct inode *inode,
 174                                  struct fsnotify_mark *inode_mark,
 175                                  struct fsnotify_mark *fanotify_mark,
 176                                  u32 mask, const void *data, int data_type,
 177                                  const unsigned char *file_name, u32 cookie)
 178 {
 179         int ret = 0;
 180         struct fanotify_event_info *event;
 181         struct fsnotify_event *fsn_event;
 182
 183         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 184         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 185         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 186         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 187         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 188         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 189         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 190         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 191         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 192         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 193
 194         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 195                                         data_type))
 196                 return 0;
 197
 198         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 199                  mask);
 200
 201         event = fanotify_alloc_event(inode, mask, data);
 202         if (unlikely(!event))
 203                 return -ENOMEM;
 204
 205         fsn_event = &event->fse;
 206         ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
 207         if (ret) {
 208                 /* Permission events shouldn't be merged */
 209                 BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
 210                 /* Our event wasn't used in the end. Free it. */
 211                 fsnotify_destroy_event(group, fsn_event);
 212
 213                 return 0;
 214         }
 215
 216 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 217         if (mask & FAN_ALL_PERM_EVENTS) {
 218                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event));
 219                 fsnotify_destroy_event(group, fsn_event);
 220         }
 221 #endif
 222         return ret;
 223 }
 224
 225 static void fanotify_free_group_priv(struct fsnotify_group *group)
 226 {
 227         struct user_struct *user;
 228
 229         user = group->fanotify_data.user;
 230         atomic_dec(&user->fanotify_listeners);
 231         free_uid(user);
 232 }
 233
 234 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 235 {
 236         struct fanotify_event_info *event;
 237
 238         event = FANOTIFY_E(fsn_event);
 239         path_put(&event->path);
 240         put_pid(event->tgid);
 241 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 242         if (fsn_event->mask & FAN_ALL_PERM_EVENTS) {
 243                 kmem_cache_free(fanotify_perm_event_cachep,
 244                                 FANOTIFY_PE(fsn_event));
 245                 return;
 246         }
 247 #endif
 248         kmem_cache_free(fanotify_event_cachep, event);
 249 }
 250
 251 const struct fsnotify_ops fanotify_fsnotify_ops = {
 252         .handle_event = fanotify_handle_event,
 253         .free_group_priv = fanotify_free_group_priv,
 254         .free_event = fanotify_free_event,
 255 };