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         /*
  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 (fanotify_is_perm_event(event->mask))
  45                 return 0;
  46
  47         list_for_each_entry_reverse(test_event, list, list) {
  48                 if (should_merge(test_event, event)) {
  49                         test_event->mask |= event->mask;
  50                         return 1;
  51                 }
  52         }
  53
  54         return 0;
  55 }
  56
  57 static int fanotify_get_response(struct fsnotify_group *group,
  58                                  struct fanotify_perm_event_info *event,
  59                                  struct fsnotify_iter_info *iter_info)
  60 {
  61         int ret;
  62
  63         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
  64
  65         wait_event(group->fanotify_data.access_waitq, event->response);
  66
  67         /* userspace responded, convert to something usable */
  68         switch (event->response) {
  69         case FAN_ALLOW:
  70                 ret = 0;
  71                 break;
  72         case FAN_DENY:
  73         default:
  74                 ret = -EPERM;
  75         }
  76         event->response = 0;
  77
  78         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  79                  group, event, ret);
  80
  81         return ret;
  82 }
  83
  84 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  85                                        struct fsnotify_mark *vfsmnt_mark,
  86                                        u32 event_mask,
  87                                        const void *data, int data_type)
  88 {
  89         __u32 marks_mask, marks_ignored_mask;
  90         const struct path *path = data;
  91
  92         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
  93                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
  94                  event_mask, data, data_type);
  95
  96         /* if we don't have enough info to send an event to userspace say no */
  97         if (data_type != FSNOTIFY_EVENT_PATH)
  98                 return false;
  99
 100         /* sorry, fanotify only gives a damn about files and dirs */
 101         if (!d_is_reg(path->dentry) &&
 102             !d_can_lookup(path->dentry))
 103                 return false;
 104
 105         if (inode_mark && vfsmnt_mark) {
 106                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 107                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 108         } else if (inode_mark) {
 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 ((event_mask & FS_EVENT_ON_CHILD) &&
 114                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 115                         return false;
 116                 marks_mask = inode_mark->mask;
 117                 marks_ignored_mask = inode_mark->ignored_mask;
 118         } else if (vfsmnt_mark) {
 119                 marks_mask = vfsmnt_mark->mask;
 120                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 121         } else {
 122                 BUG();
 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         if (fanotify_is_perm_event(mask)) {
 142                 struct fanotify_perm_event_info *pevent;
 143
 144                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 145                                           GFP_KERNEL);
 146                 if (!pevent)
 147                         return NULL;
 148                 event = &pevent->fae;
 149                 pevent->response = 0;
 150                 goto init;
 151         }
 152         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 153         if (!event)
 154                 return NULL;
 155 init: __maybe_unused
 156         fsnotify_init_event(&event->fse, inode, mask);
 157         event->tgid = get_pid(task_tgid(current));
 158         if (path) {
 159                 event->path = *path;
 160                 path_get(&event->path);
 161         } else {
 162                 event->path.mnt = NULL;
 163                 event->path.dentry = NULL;
 164         }
 165         return event;
 166 }
 167
 168 static int fanotify_handle_event(struct fsnotify_group *group,
 169                                  struct inode *inode,
 170                                  struct fsnotify_mark *inode_mark,
 171                                  struct fsnotify_mark *fanotify_mark,
 172                                  u32 mask, const void *data, int data_type,
 173                                  const unsigned char *file_name, u32 cookie,
 174                                  struct fsnotify_iter_info *iter_info)
 175 {
 176         int ret = 0;
 177         struct fanotify_event_info *event;
 178         struct fsnotify_event *fsn_event;
 179
 180         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 181         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 182         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 183         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 184         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 185         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 186         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 187         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 188         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 189         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 190
 191         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 192                                         data_type))
 193                 return 0;
 194
 195         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 196                  mask);
 197
 198         if (fanotify_is_perm_event(mask)) {
 199                 /*
 200                  * fsnotify_prepare_user_wait() fails if we race with mark
 201                  * deletion.  Just let the operation pass in that case.
 202                  */
 203                 if (!fsnotify_prepare_user_wait(iter_info))
 204                         return 0;
 205         }
 206
 207         event = fanotify_alloc_event(inode, mask, data);
 208         ret = -ENOMEM;
 209         if (unlikely(!event))
 210                 goto finish;
 211
 212         fsn_event = &event->fse;
 213         ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
 214         if (ret) {
 215                 /* Permission events shouldn't be merged */
 216                 BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
 217                 /* Our event wasn't used in the end. Free it. */
 218                 fsnotify_destroy_event(group, fsn_event);
 219
 220                 ret = 0;
 221         } else if (fanotify_is_perm_event(mask)) {
 222                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 223                                             iter_info);
 224                 fsnotify_destroy_event(group, fsn_event);
 225         }
 226 finish:
 227         if (fanotify_is_perm_event(mask))
 228                 fsnotify_finish_user_wait(iter_info);
 229
 230         return ret;
 231 }
 232
 233 static void fanotify_free_group_priv(struct fsnotify_group *group)
 234 {
 235         struct user_struct *user;
 236
 237         user = group->fanotify_data.user;
 238         atomic_dec(&user->fanotify_listeners);
 239         free_uid(user);
 240 }
 241
 242 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 243 {
 244         struct fanotify_event_info *event;
 245
 246         event = FANOTIFY_E(fsn_event);
 247         path_put(&event->path);
 248         put_pid(event->tgid);
 249         if (fanotify_is_perm_event(fsn_event->mask)) {
 250                 kmem_cache_free(fanotify_perm_event_cachep,
 251                                 FANOTIFY_PE(fsn_event));
 252                 return;
 253         }
 254         kmem_cache_free(fanotify_event_cachep, event);
 255 }
 256
 257 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 258 {
 259         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 260 }
 261
 262 const struct fsnotify_ops fanotify_fsnotify_ops = {
 263         .handle_event = fanotify_handle_event,
 264         .free_group_priv = fanotify_free_group_priv,
 265         .free_event = fanotify_free_event,
 266         .free_mark = fanotify_free_mark,
 267 };