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 #include <linux/audit.h>
  14
  15 #include "fanotify.h"
  16
  17 static bool should_merge(struct fsnotify_event *old_fsn,
  18                          struct fsnotify_event *new_fsn)
  19 {
  20         struct fanotify_event_info *old, *new;
  21
  22         pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
  23         old = FANOTIFY_E(old_fsn);
  24         new = FANOTIFY_E(new_fsn);
  25
  26         if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
  27             old->path.mnt == new->path.mnt &&
  28             old->path.dentry == new->path.dentry)
  29                 return true;
  30         return false;
  31 }
  32
  33 /* and the list better be locked by something too! */
  34 static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
  35 {
  36         struct fsnotify_event *test_event;
  37
  38         pr_debug("%s: list=%p event=%p\n", __func__, list, event);
  39
  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 (fanotify_is_perm_event(event->mask))
  46                 return 0;
  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 static int fanotify_get_response(struct fsnotify_group *group,
  59                                  struct fanotify_perm_event_info *event,
  60                                  struct fsnotify_iter_info *iter_info)
  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 & ~FAN_AUDIT) {
  70         case FAN_ALLOW:
  71                 ret = 0;
  72                 break;
  73         case FAN_DENY:
  74         default:
  75                 ret = -EPERM;
  76         }
  77
  78         /* Check if the response should be audited */
  79         if (event->response & FAN_AUDIT)
  80                 audit_fanotify(event->response & ~FAN_AUDIT);
  81
  82         event->response = 0;
  83
  84         pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
  85                  group, event, ret);
  86
  87         return ret;
  88 }
  89
  90 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
  91                                        struct fsnotify_mark *vfsmnt_mark,
  92                                        u32 event_mask,
  93                                        const void *data, int data_type)
  94 {
  95         __u32 marks_mask, marks_ignored_mask;
  96         const struct path *path = data;
  97
  98         pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
  99                  " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
 100                  event_mask, data, data_type);
 101
 102         /* if we don't have enough info to send an event to userspace say no */
 103         if (data_type != FSNOTIFY_EVENT_PATH)
 104                 return false;
 105
 106         /* sorry, fanotify only gives a damn about files and dirs */
 107         if (!d_is_reg(path->dentry) &&
 108             !d_can_lookup(path->dentry))
 109                 return false;
 110
 111         if (inode_mark && vfsmnt_mark) {
 112                 marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
 113                 marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
 114         } else if (inode_mark) {
 115                 /*
 116                  * if the event is for a child and this inode doesn't care about
 117                  * events on the child, don't send it!
 118                  */
 119                 if ((event_mask & FS_EVENT_ON_CHILD) &&
 120                     !(inode_mark->mask & FS_EVENT_ON_CHILD))
 121                         return false;
 122                 marks_mask = inode_mark->mask;
 123                 marks_ignored_mask = inode_mark->ignored_mask;
 124         } else if (vfsmnt_mark) {
 125                 marks_mask = vfsmnt_mark->mask;
 126                 marks_ignored_mask = vfsmnt_mark->ignored_mask;
 127         } else {
 128                 BUG();
 129         }
 130
 131         if (d_is_dir(path->dentry) &&
 132             !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 133                 return false;
 134
 135         if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
 136                                  ~marks_ignored_mask)
 137                 return true;
 138
 139         return false;
 140 }
 141
 142 struct fanotify_event_info *fanotify_alloc_event(struct inode *inode, u32 mask,
 143                                                  const struct path *path)
 144 {
 145         struct fanotify_event_info *event;
 146
 147         if (fanotify_is_perm_event(mask)) {
 148                 struct fanotify_perm_event_info *pevent;
 149
 150                 pevent = kmem_cache_alloc(fanotify_perm_event_cachep,
 151                                           GFP_KERNEL);
 152                 if (!pevent)
 153                         return NULL;
 154                 event = &pevent->fae;
 155                 pevent->response = 0;
 156                 goto init;
 157         }
 158         event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
 159         if (!event)
 160                 return NULL;
 161 init: __maybe_unused
 162         fsnotify_init_event(&event->fse, inode, mask);
 163         event->tgid = get_pid(task_tgid(current));
 164         if (path) {
 165                 event->path = *path;
 166                 path_get(&event->path);
 167         } else {
 168                 event->path.mnt = NULL;
 169                 event->path.dentry = NULL;
 170         }
 171         return event;
 172 }
 173
 174 static int fanotify_handle_event(struct fsnotify_group *group,
 175                                  struct inode *inode,
 176                                  struct fsnotify_mark *inode_mark,
 177                                  struct fsnotify_mark *fanotify_mark,
 178                                  u32 mask, const void *data, int data_type,
 179                                  const unsigned char *file_name, u32 cookie,
 180                                  struct fsnotify_iter_info *iter_info)
 181 {
 182         int ret = 0;
 183         struct fanotify_event_info *event;
 184         struct fsnotify_event *fsn_event;
 185
 186         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
 187         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
 188         BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
 189         BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
 190         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
 191         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
 192         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 193         BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 194         BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 195         BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 196
 197         if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
 198                                         data_type))
 199                 return 0;
 200
 201         pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
 202                  mask);
 203
 204         if (fanotify_is_perm_event(mask)) {
 205                 /*
 206                  * fsnotify_prepare_user_wait() fails if we race with mark
 207                  * deletion.  Just let the operation pass in that case.
 208                  */
 209                 if (!fsnotify_prepare_user_wait(iter_info))
 210                         return 0;
 211         }
 212
 213         event = fanotify_alloc_event(inode, mask, data);
 214         ret = -ENOMEM;
 215         if (unlikely(!event))
 216                 goto finish;
 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                 ret = 0;
 227         } else if (fanotify_is_perm_event(mask)) {
 228                 ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
 229                                             iter_info);
 230                 fsnotify_destroy_event(group, fsn_event);
 231         }
 232 finish:
 233         if (fanotify_is_perm_event(mask))
 234                 fsnotify_finish_user_wait(iter_info);
 235
 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         if (fanotify_is_perm_event(fsn_event->mask)) {
 256                 kmem_cache_free(fanotify_perm_event_cachep,
 257                                 FANOTIFY_PE(fsn_event));
 258                 return;
 259         }
 260         kmem_cache_free(fanotify_event_cachep, event);
 261 }
 262
 263 static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 264 {
 265         kmem_cache_free(fanotify_mark_cache, fsn_mark);
 266 }
 267
 268 const struct fsnotify_ops fanotify_fsnotify_ops = {
 269         .handle_event = fanotify_handle_event,
 270         .free_group_priv = fanotify_free_group_priv,
 271         .free_event = fanotify_free_event,
 272         .free_mark = fanotify_free_mark,
 273 };