// SPDX-License-Identifier: GPL-2.0
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#include <linux/fanotify.h>
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#include <linux/fdtable.h>
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#include <linux/fsnotify_backend.h>
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#include <linux/init.h>
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#include <linux/jiffies.h>
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#include <linux/kernel.h> /* UINT_MAX */
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#include <linux/mount.h>
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#include <linux/sched.h>
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#include <linux/sched/user.h>
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#include <linux/sched/signal.h>
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#include <linux/types.h>
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#include <linux/wait.h>
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#include <linux/audit.h>
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#include <linux/sched/mm.h>
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#include "fanotify.h"
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static bool should_merge(struct fsnotify_event *old_fsn,
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struct fsnotify_event *new_fsn)
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{
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struct fanotify_event_info *old, *new;
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pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
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old = FANOTIFY_E(old_fsn);
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new = FANOTIFY_E(new_fsn);
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if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
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old->path.mnt == new->path.mnt &&
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old->path.dentry == new->path.dentry)
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return true;
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return false;
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}
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/* and the list better be locked by something too! */
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static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
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{
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struct fsnotify_event *test_event;
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pr_debug("%s: list=%p event=%p\n", __func__, list, event);
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/*
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* Don't merge a permission event with any other event so that we know
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* the event structure we have created in fanotify_handle_event() is the
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* one we should check for permission response.
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*/
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if (fanotify_is_perm_event(event->mask))
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return 0;
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list_for_each_entry_reverse(test_event, list, list) {
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if (should_merge(test_event, event)) {
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test_event->mask |= event->mask;
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return 1;
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}
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}
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return 0;
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}
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static int fanotify_get_response(struct fsnotify_group *group,
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struct fanotify_perm_event_info *event,
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struct fsnotify_iter_info *iter_info)
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{
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int ret;
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pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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wait_event(group->fanotify_data.access_waitq, event->response);
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/* userspace responded, convert to something usable */
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switch (event->response & ~FAN_AUDIT) {
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case FAN_ALLOW:
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ret = 0;
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break;
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case FAN_DENY:
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default:
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ret = -EPERM;
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}
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/* Check if the response should be audited */
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if (event->response & FAN_AUDIT)
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audit_fanotify(event->response & ~FAN_AUDIT);
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event->response = 0;
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pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
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group, event, ret);
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return ret;
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}
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static bool fanotify_should_send_event(struct fsnotify_iter_info *iter_info,
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u32 event_mask, const void *data,
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int data_type)
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{
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__u32 marks_mask = 0, marks_ignored_mask = 0;
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const struct path *path = data;
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struct fsnotify_mark *mark;
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int type;
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pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
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__func__, iter_info->report_mask, event_mask, data, data_type);
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/* if we don't have enough info to send an event to userspace say no */
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if (data_type != FSNOTIFY_EVENT_PATH)
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return false;
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/* sorry, fanotify only gives a damn about files and dirs */
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if (!d_is_reg(path->dentry) &&
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!d_can_lookup(path->dentry))
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return false;
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fsnotify_foreach_obj_type(type) {
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if (!fsnotify_iter_should_report_type(iter_info, type))
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continue;
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mark = iter_info->marks[type];
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/* Apply ignore mask regardless of ISDIR and ON_CHILD flags */
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marks_ignored_mask |= mark->ignored_mask;
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/*
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* If the event is for a child and this mark doesn't care about
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* events on a child, don't send it!
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*/
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if (event_mask & FS_EVENT_ON_CHILD &&
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(type != FSNOTIFY_OBJ_TYPE_INODE ||
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!(mark->mask & FS_EVENT_ON_CHILD)))
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continue;
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marks_mask |= mark->mask;
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}
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if (d_is_dir(path->dentry) &&
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!(marks_mask & FS_ISDIR & ~marks_ignored_mask))
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return false;
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if (event_mask & FAN_ALL_OUTGOING_EVENTS & marks_mask &
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~marks_ignored_mask)
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return true;
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return false;
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}
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struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
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struct inode *inode, u32 mask,
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const struct path *path)
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{
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struct fanotify_event_info *event = NULL;
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gfp_t gfp = GFP_KERNEL_ACCOUNT;
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/*
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* For queues with unlimited length lost events are not expected and
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* can possibly have security implications. Avoid losing events when
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* memory is short. For the limited size queues, avoid OOM killer in the
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* target monitoring memcg as it may have security repercussion.
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*/
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if (group->max_events == UINT_MAX)
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gfp |= __GFP_NOFAIL;
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else
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gfp |= __GFP_RETRY_MAYFAIL;
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/* Whoever is interested in the event, pays for the allocation. */
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memalloc_use_memcg(group->memcg);
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if (fanotify_is_perm_event(mask)) {
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struct fanotify_perm_event_info *pevent;
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pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
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if (!pevent)
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goto out;
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event = &pevent->fae;
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pevent->response = 0;
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goto init;
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}
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event = kmem_cache_alloc(fanotify_event_cachep, gfp);
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if (!event)
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goto out;
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init: __maybe_unused
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fsnotify_init_event(&event->fse, inode, mask);
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event->tgid = get_pid(task_tgid(current));
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if (path) {
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event->path = *path;
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path_get(&event->path);
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} else {
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event->path.mnt = NULL;
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event->path.dentry = NULL;
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}
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out:
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memalloc_unuse_memcg();
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return event;
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}
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static int fanotify_handle_event(struct fsnotify_group *group,
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struct inode *inode,
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u32 mask, const void *data, int data_type,
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const unsigned char *file_name, u32 cookie,
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struct fsnotify_iter_info *iter_info)
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{
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int ret = 0;
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struct fanotify_event_info *event;
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struct fsnotify_event *fsn_event;
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BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
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BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
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BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
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BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
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BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
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BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
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BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
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BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
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BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
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BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
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if (!fanotify_should_send_event(iter_info, mask, data, data_type))
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return 0;
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pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
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mask);
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if (fanotify_is_perm_event(mask)) {
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/*
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* fsnotify_prepare_user_wait() fails if we race with mark
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* deletion. Just let the operation pass in that case.
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*/
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if (!fsnotify_prepare_user_wait(iter_info))
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return 0;
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}
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event = fanotify_alloc_event(group, inode, mask, data);
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ret = -ENOMEM;
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if (unlikely(!event)) {
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/*
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* We don't queue overflow events for permission events as
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* there the access is denied and so no event is in fact lost.
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*/
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if (!fanotify_is_perm_event(mask))
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fsnotify_queue_overflow(group);
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goto finish;
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}
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fsn_event = &event->fse;
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ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
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if (ret) {
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/* Permission events shouldn't be merged */
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BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
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/* Our event wasn't used in the end. Free it. */
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fsnotify_destroy_event(group, fsn_event);
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ret = 0;
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} else if (fanotify_is_perm_event(mask)) {
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ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
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iter_info);
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fsnotify_destroy_event(group, fsn_event);
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}
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finish:
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if (fanotify_is_perm_event(mask))
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fsnotify_finish_user_wait(iter_info);
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return ret;
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}
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static void fanotify_free_group_priv(struct fsnotify_group *group)
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{
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struct user_struct *user;
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user = group->fanotify_data.user;
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atomic_dec(&user->fanotify_listeners);
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free_uid(user);
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}
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static void fanotify_free_event(struct fsnotify_event *fsn_event)
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{
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struct fanotify_event_info *event;
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event = FANOTIFY_E(fsn_event);
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path_put(&event->path);
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put_pid(event->tgid);
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if (fanotify_is_perm_event(fsn_event->mask)) {
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kmem_cache_free(fanotify_perm_event_cachep,
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FANOTIFY_PE(fsn_event));
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return;
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}
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kmem_cache_free(fanotify_event_cachep, event);
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}
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static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
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{
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kmem_cache_free(fanotify_mark_cache, fsn_mark);
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}
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const struct fsnotify_ops fanotify_fsnotify_ops = {
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.handle_event = fanotify_handle_event,
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.free_group_priv = fanotify_free_group_priv,
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.free_event = fanotify_free_event,
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.free_mark = fanotify_free_mark,
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};
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