fs/notify/fanotify/fanotify.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/fanotify.h>
   3 #include <linux/fdtable.h>
   4 #include <linux/fsnotify_backend.h>
   5 #include <linux/init.h>
   6 #include <linux/jiffies.h>
   7 #include <linux/kernel.h> /* UINT_MAX */
   8 #include <linux/mount.h>
   9 #include <linux/sched.h>
  10 #include <linux/sched/user.h>
  11 #include <linux/types.h>
  12 #include <linux/wait.h>
  13
  14 #include "fanotify.h"
  15
  16 static bool should_merge(struct fsnotify_event *old_fsn,
  17                          struct fsnotify_event *new_fsn)
  18 {
  19         struct fanotify_event_info *old, *new;
  20
  21         pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
  22         old = FANOTIFY_E(old_fsn);
  23         new = FANOTIFY_E(new_fsn);
  24
  25         if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
  26             old->path.mnt == new->path.mnt &&
  27             old->path.dentry == new->path.dentry)
  28                 return true;
  29         return false;
  30 }
  31
  32 /* and the list better be locked by something too! */
  33 static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
  34 {
  35         struct fsnotify_event *test_event;
  36
  37         pr_debug("%s: list=%p event=%p\n", __func__, list, event);
  38
  39 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
  40         /*
  41          * Don't merge a permission event with any other event so that we know
  42          * the event structure we have created in fanotify_handle_event() is the
  43          * one we should check for permission response.
  44          */
  45         if (event->mask & FAN_ALL_PERM_EVENTS)
  46                 return 0;
  47 #endif
  48
  49         list_for_each_entry_reverse(test_event, list, list) {
  50                 if (should_merge(test_event, event)) {
  51                         test_event->mask |= event->mask;
  52                         return 1;
  53                 }
  54         }
  55
  56         return 0;
  57 }
  58
  59 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
  60 static int fanotify_get_response(struct fsnotify_group *group,
  61                                  struct fanotify_perm_event_info *event,
  62                                  struct fsnotify_iter_info *iter_info)
  63 {
  64         int ret;
  65
  66         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  67
  68         wait_event(group->fanotify_data.access_waitq, event->response);
  69
  70         /* userspace responded, convert to something usable */
  71         switch (event->response) {
  72         case FAN_ALLOW:
  73                 ret = 0;
  74                 break;
  75         case FAN_DENY:
  76         default:
  77                 ret = -EPERM;
  78         }
  79         event->response = 0;
  80
  81         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  82                  group, event, ret);
  83
  84         return ret;
  85 }
  86 #endif
  87
  88 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  89                                        struct fsnotify_mark *vfsmnt_mark,
  90                                        u32 event_mask,
  91                                        const void *data, int data_type)
  92 {
  93         __u32 marks_mask = 0, marks_ignored_mask = 0;
  94         const struct path *path = data;
  95
  96         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
  97                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
  98                  event_mask, data, data_type);
  99
 100         /* if we don't have enough info to send an event to userspace say no */
 101         if (data_type != FSNOTIFY_EVENT_PATH)
 102                 return false;
 103
 104         /* sorry, fanotify only gives a damn about files and dirs */
 105         if (!d_is_reg(path->dentry) &&
 106             !d_can_lookup(path->dentry))
 107                 return false;
 108
 109         /*
 110          * if the event is for a child and this inode doesn't care about
 111          * events on the child, don't send it!
 112          */
 113         if (inode_mark &&
 114             (!(event_mask & FS_EVENT_ON_CHILD) ||
 115              (inode_mark->mask & FS_EVENT_ON_CHILD))) {
 116                 marks_mask |= inode_mark->mask;
 117                 marks_ignored_mask |= inode_mark->ignored_mask;
 118         }
 119
 120         if (vfsmnt_mark) {
 121                 marks_mask |= vfsmnt_mark->mask;
 122                 marks_ignored_mask |= vfsmnt_mark->ignored_mask;
 123         }
 124
 125         if (d_is_dir(path->dentry) &&
 126             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 127                 return false;
 128
 129         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 130                                  ~marks_ignored_mask)
 131                 return true;
 132
 133         return false;
 134 }
 135
 136 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 137                                                  const struct path *path)
 138 {
 139         struct fanotify_event_info *event;
 140
 141 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 142         if (mask & FAN_ALL_PERM_EVENTS) {
 143                 struct fanotify_perm_event_info *pevent;
 144
 145                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 146                                           GFP_KERNEL);
 147                 if (!pevent)
 148                         return NULL;
 149                 event = &pevent->fae;
 150                 pevent->response = 0;
 151                 goto init;
 152         }
 153 #endif
 154         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 155         if (!event)
 156                 return NULL;
 157 init: __maybe_unused
 158         fsnotify_init_event(&event->fse, inode, mask);
 159         event->tgid = get_pid(task_tgid(current));
 160         if (path) {
 161                 event->path = *path;
 162                 path_get(&event->path);
 163         } else {
 164                 event->path.mnt = NULL;
 165                 event->path.dentry = NULL;
 166         }
 167         return event;
 168 }
 169
 170 static int fanotify_handle_event(struct fsnotify_group *group,
 171                                  struct inode *inode,
 172                                  struct fsnotify_mark *inode_mark,
 173                                  struct fsnotify_mark *fanotify_mark,
 174                                  u32 mask, const void *data, int data_type,
 175                                  const unsigned char *file_name, u32 cookie,
 176                                  struct fsnotify_iter_info *iter_info)
 177 {
 178         int ret = 0;
 179         struct fanotify_event_info *event;
 180         struct fsnotify_event *fsn_event;
 181
 182         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 183         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 184         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 185         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 186         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 187         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 188         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 189         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 190         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 191         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 192
 193         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 194                                         data_type))
 195                 return 0;
 196
 197         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 198                  mask);
 199
 200 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 201         if (mask & FAN_ALL_PERM_EVENTS) {
 202                 /*
 203                  * fsnotify_prepare_user_wait() fails if we race with mark
 204                  * deletion.  Just let the operation pass in that case.
 205                  */
 206                 if (!fsnotify_prepare_user_wait(iter_info))
 207                         return 0;
 208         }
 209 #endif
 210
 211         event = fanotify_alloc_event(inode, mask, data);
 212         ret = -ENOMEM;
 213         if (unlikely(!event))
 214                 goto finish;
 215
 216         fsn_event = &event->fse;
 217         ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
 218         if (ret) {
 219                 /* Permission events shouldn't be merged */
 220                 BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
 221                 /* Our event wasn't used in the end. Free it. */
 222                 fsnotify_destroy_event(group, fsn_event);
 223
 224                 ret = 0;
 225                 goto finish;
 226         }
 227
 228 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 229         if (mask & FAN_ALL_PERM_EVENTS) {
 230                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 231                                             iter_info);
 232                 fsnotify_destroy_event(group, fsn_event);
 233         }
 234 finish:
 235         if (mask & FAN_ALL_PERM_EVENTS)
 236                 fsnotify_finish_user_wait(iter_info);
 237 #else
 238 finish:
 239 #endif
 240         return ret;
 241 }
 242
 243 static void fanotify_free_group_priv(struct fsnotify_group *group)
 244 {
 245         struct user_struct *user;
 246
 247         user = group->fanotify_data.user;
 248         atomic_dec(&user->fanotify_listeners);
 249         free_uid(user);
 250 }
 251
 252 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 253 {
 254         struct fanotify_event_info *event;
 255
 256         event = FANOTIFY_E(fsn_event);
 257         path_put(&event->path);
 258         put_pid(event->tgid);
 259 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 260         if (fsn_event->mask & FAN_ALL_PERM_EVENTS) {
 261                 kmem_cache_free(fanotify_perm_event_cachep,
 262                                 FANOTIFY_PE(fsn_event));
 263                 return;
 264         }
 265 #endif
 266         kmem_cache_free(fanotify_event_cachep, event);
 267 }
 268
 269 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 270 {
 271         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 272 }
 273
 274 const struct fsnotify_ops fanotify_fsnotify_ops = {
 275         .handle_event = fanotify_handle_event,
 276         .free_group_priv = fanotify_free_group_priv,
 277         .free_event = fanotify_free_event,
 278         .free_mark = fanotify_free_mark,
 279 };