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         /*
  69          * fsnotify_prepare_user_wait() fails if we race with mark deletion.
  70          * Just let the operation pass in that case.
  71          */
  72         if (!fsnotify_prepare_user_wait(iter_info)) {
  73                 event->response = FAN_ALLOW;
  74                 goto out;
  75         }
  76
  77         wait_event(group->fanotify_data.access_waitq, event->response);
  78
  79         fsnotify_finish_user_wait(iter_info);
  80 out:
  81         /* userspace responded, convert to something usable */
  82         switch (event->response) {
  83         case FAN_ALLOW:
  84                 ret = 0;
  85                 break;
  86         case FAN_DENY:
  87         default:
  88                 ret = -EPERM;
  89         }
  90         event->response = 0;
  91
  92         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  93                  group, event, ret);
  94
  95         return ret;
  96 }
  97 #endif
  98
  99 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
 100                                        struct fsnotify_mark *vfsmnt_mark,
 101                                        u32 event_mask,
 102                                        const void *data, int data_type)
 103 {
 104         __u32 marks_mask, marks_ignored_mask;
 105         const struct path *path = data;
 106
 107         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
 108                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
 109                  event_mask, data, data_type);
 110
 111         /* if we don't have enough info to send an event to userspace say no */
 112         if (data_type != FSNOTIFY_EVENT_PATH)
 113                 return false;
 114
 115         /* sorry, fanotify only gives a damn about files and dirs */
 116         if (!d_is_reg(path->dentry) &&
 117             !d_can_lookup(path->dentry))
 118                 return false;
 119
 120         if (inode_mark && vfsmnt_mark) {
 121                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 122                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 123         } else if (inode_mark) {
 124                 /*
 125                  * if the event is for a child and this inode doesn't care about
 126                  * events on the child, don't send it!
 127                  */
 128                 if ((event_mask & FS_EVENT_ON_CHILD) &&
 129                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 130                         return false;
 131                 marks_mask = inode_mark->mask;
 132                 marks_ignored_mask = inode_mark->ignored_mask;
 133         } else if (vfsmnt_mark) {
 134                 marks_mask = vfsmnt_mark->mask;
 135                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 136         } else {
 137                 BUG();
 138         }
 139
 140         if (d_is_dir(path->dentry) &&
 141             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 142                 return false;
 143
 144         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 145                                  ~marks_ignored_mask)
 146                 return true;
 147
 148         return false;
 149 }
 150
 151 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 152                                                  const struct path *path)
 153 {
 154         struct fanotify_event_info *event;
 155
 156 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 157         if (mask & FAN_ALL_PERM_EVENTS) {
 158                 struct fanotify_perm_event_info *pevent;
 159
 160                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 161                                           GFP_KERNEL);
 162                 if (!pevent)
 163                         return NULL;
 164                 event = &pevent->fae;
 165                 pevent->response = 0;
 166                 goto init;
 167         }
 168 #endif
 169         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 170         if (!event)
 171                 return NULL;
 172 init: __maybe_unused
 173         fsnotify_init_event(&event->fse, inode, mask);
 174         event->tgid = get_pid(task_tgid(current));
 175         if (path) {
 176                 event->path = *path;
 177                 path_get(&event->path);
 178         } else {
 179                 event->path.mnt = NULL;
 180                 event->path.dentry = NULL;
 181         }
 182         return event;
 183 }
 184
 185 static int fanotify_handle_event(struct fsnotify_group *group,
 186                                  struct inode *inode,
 187                                  struct fsnotify_mark *inode_mark,
 188                                  struct fsnotify_mark *fanotify_mark,
 189                                  u32 mask, const void *data, int data_type,
 190                                  const unsigned char *file_name, u32 cookie,
 191                                  struct fsnotify_iter_info *iter_info)
 192 {
 193         int ret = 0;
 194         struct fanotify_event_info *event;
 195         struct fsnotify_event *fsn_event;
 196
 197         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 198         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 199         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 200         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 201         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 202         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 203         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 204         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 205         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 206         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 207
 208         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 209                                         data_type))
 210                 return 0;
 211
 212         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 213                  mask);
 214
 215         event = fanotify_alloc_event(inode, mask, data);
 216         if (unlikely(!event))
 217                 return -ENOMEM;
 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                 return 0;
 228         }
 229
 230 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 231         if (mask & FAN_ALL_PERM_EVENTS) {
 232                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 233                                             iter_info);
 234                 fsnotify_destroy_event(group, fsn_event);
 235         }
 236 #endif
 237         return ret;
 238 }
 239
 240 static void fanotify_free_group_priv(struct fsnotify_group *group)
 241 {
 242         struct user_struct *user;
 243
 244         user = group->fanotify_data.user;
 245         atomic_dec(&user->fanotify_listeners);
 246         free_uid(user);
 247 }
 248
 249 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 250 {
 251         struct fanotify_event_info *event;
 252
 253         event = FANOTIFY_E(fsn_event);
 254         path_put(&event->path);
 255         put_pid(event->tgid);
 256 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 257         if (fsn_event->mask & FAN_ALL_PERM_EVENTS) {
 258                 kmem_cache_free(fanotify_perm_event_cachep,
 259                                 FANOTIFY_PE(fsn_event));
 260                 return;
 261         }
 262 #endif
 263         kmem_cache_free(fanotify_event_cachep, event);
 264 }
 265
 266 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 267 {
 268         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 269 }
 270
 271 const struct fsnotify_ops fanotify_fsnotify_ops = {
 272         .handle_event = fanotify_handle_event,
 273         .free_group_priv = fanotify_free_group_priv,
 274         .free_event = fanotify_free_event,
 275         .free_mark = fanotify_free_mark,
 276 };