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         /*
  68          * fsnotify_prepare_user_wait() fails if we race with mark deletion.
  69          * Just let the operation pass in that case.
  70          */
  71         if (!fsnotify_prepare_user_wait(iter_info)) {
  72                 event->response = FAN_ALLOW;
  73                 goto out;
  74         }
  75
  76         wait_event(group->fanotify_data.access_waitq, event->response);
  77
  78         fsnotify_finish_user_wait(iter_info);
  79 out:
  80         /* userspace responded, convert to something usable */
  81         switch (event->response) {
  82         case FAN_ALLOW:
  83                 ret = 0;
  84                 break;
  85         case FAN_DENY:
  86         default:
  87                 ret = -EPERM;
  88         }
  89         event->response = 0;
  90
  91         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  92                  group, event, ret);
  93
  94         return ret;
  95 }
  96 #endif
  97
  98 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  99                                        struct fsnotify_mark *vfsmnt_mark,
 100                                        u32 event_mask,
 101                                        const void *data, int data_type)
 102 {
 103         __u32 marks_mask, marks_ignored_mask;
 104         const struct path *path = data;
 105
 106         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
 107                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
 108                  event_mask, data, data_type);
 109
 110         /* if we don't have enough info to send an event to userspace say no */
 111         if (data_type != FSNOTIFY_EVENT_PATH)
 112                 return false;
 113
 114         /* sorry, fanotify only gives a damn about files and dirs */
 115         if (!d_is_reg(path->dentry) &&
 116             !d_can_lookup(path->dentry))
 117                 return false;
 118
 119         if (inode_mark && vfsmnt_mark) {
 120                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 121                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 122         } else if (inode_mark) {
 123                 /*
 124                  * if the event is for a child and this inode doesn't care about
 125                  * events on the child, don't send it!
 126                  */
 127                 if ((event_mask & FS_EVENT_ON_CHILD) &&
 128                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 129                         return false;
 130                 marks_mask = inode_mark->mask;
 131                 marks_ignored_mask = inode_mark->ignored_mask;
 132         } else if (vfsmnt_mark) {
 133                 marks_mask = vfsmnt_mark->mask;
 134                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 135         } else {
 136                 BUG();
 137         }
 138
 139         if (d_is_dir(path->dentry) &&
 140             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 141                 return false;
 142
 143         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 144                                  ~marks_ignored_mask)
 145                 return true;
 146
 147         return false;
 148 }
 149
 150 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 151                                                  const struct path *path)
 152 {
 153         struct fanotify_event_info *event;
 154
 155 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 156         if (mask & FAN_ALL_PERM_EVENTS) {
 157                 struct fanotify_perm_event_info *pevent;
 158
 159                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 160                                           GFP_KERNEL);
 161                 if (!pevent)
 162                         return NULL;
 163                 event = &pevent->fae;
 164                 pevent->response = 0;
 165                 goto init;
 166         }
 167 #endif
 168         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 169         if (!event)
 170                 return NULL;
 171 init: __maybe_unused
 172         fsnotify_init_event(&event->fse, inode, mask);
 173         event->tgid = get_pid(task_tgid(current));
 174         if (path) {
 175                 event->path = *path;
 176                 path_get(&event->path);
 177         } else {
 178                 event->path.mnt = NULL;
 179                 event->path.dentry = NULL;
 180         }
 181         return event;
 182 }
 183
 184 static int fanotify_handle_event(struct fsnotify_group *group,
 185                                  struct inode *inode,
 186                                  struct fsnotify_mark *inode_mark,
 187                                  struct fsnotify_mark *fanotify_mark,
 188                                  u32 mask, const void *data, int data_type,
 189                                  const unsigned char *file_name, u32 cookie,
 190                                  struct fsnotify_iter_info *iter_info)
 191 {
 192         int ret = 0;
 193         struct fanotify_event_info *event;
 194         struct fsnotify_event *fsn_event;
 195
 196         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 197         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 198         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 199         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 200         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 201         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 202         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 203         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 204         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 205         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 206
 207         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 208                                         data_type))
 209                 return 0;
 210
 211         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 212                  mask);
 213
 214         event = fanotify_alloc_event(inode, mask, data);
 215         if (unlikely(!event))
 216                 return -ENOMEM;
 217
 218         fsn_event = &event->fse;
 219         ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
 220         if (ret) {
 221                 /* Permission events shouldn't be merged */
 222                 BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
 223                 /* Our event wasn't used in the end. Free it. */
 224                 fsnotify_destroy_event(group, fsn_event);
 225
 226                 return 0;
 227         }
 228
 229 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 230         if (mask & FAN_ALL_PERM_EVENTS) {
 231                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 232                                             iter_info);
 233                 fsnotify_destroy_event(group, fsn_event);
 234         }
 235 #endif
 236         return ret;
 237 }
 238
 239 static void fanotify_free_group_priv(struct fsnotify_group *group)
 240 {
 241         struct user_struct *user;
 242
 243         user = group->fanotify_data.user;
 244         atomic_dec(&user->fanotify_listeners);
 245         free_uid(user);
 246 }
 247
 248 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 249 {
 250         struct fanotify_event_info *event;
 251
 252         event = FANOTIFY_E(fsn_event);
 253         path_put(&event->path);
 254         put_pid(event->tgid);
 255 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 256         if (fsn_event->mask & FAN_ALL_PERM_EVENTS) {
 257                 kmem_cache_free(fanotify_perm_event_cachep,
 258                                 FANOTIFY_PE(fsn_event));
 259                 return;
 260         }
 261 #endif
 262         kmem_cache_free(fanotify_event_cachep, event);
 263 }
 264
 265 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 266 {
 267         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 268 }
 269
 270 const struct fsnotify_ops fanotify_fsnotify_ops = {
 271         .handle_event = fanotify_handle_event,
 272         .free_group_priv = fanotify_free_group_priv,
 273         .free_event = fanotify_free_event,
 274         .free_mark = fanotify_free_mark,
 275 };