// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Directory notifications for Linux.
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*
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* Copyright (C) 2000,2001,2002 Stephen Rothwell
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*
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* Copyright (C) 2009 Eric Paris <Red Hat Inc>
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* dnotify was largly rewritten to use the new fsnotify infrastructure
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*/
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#include <linux/fs.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/sched/signal.h>
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#include <linux/dnotify.h>
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#include <linux/init.h>
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#include <linux/security.h>
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#include <linux/spinlock.h>
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#include <linux/slab.h>
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#include <linux/fdtable.h>
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#include <linux/fsnotify_backend.h>
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int dir_notify_enable __read_mostly = 1;
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static struct kmem_cache *dnotify_struct_cache __read_mostly;
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static struct kmem_cache *dnotify_mark_cache __read_mostly;
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static struct fsnotify_group *dnotify_group __read_mostly;
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/*
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* dnotify will attach one of these to each inode (i_fsnotify_marks) which
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* is being watched by dnotify. If multiple userspace applications are watching
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* the same directory with dnotify their information is chained in dn
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*/
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struct dnotify_mark {
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struct fsnotify_mark fsn_mark;
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struct dnotify_struct *dn;
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};
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/*
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* When a process starts or stops watching an inode the set of events which
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* dnotify cares about for that inode may change. This function runs the
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* list of everything receiving dnotify events about this directory and calculates
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* the set of all those events. After it updates what dnotify is interested in
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* it calls the fsnotify function so it can update the set of all events relevant
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* to this inode.
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*/
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static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
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{
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__u32 new_mask = 0;
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struct dnotify_struct *dn;
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struct dnotify_mark *dn_mark = container_of(fsn_mark,
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struct dnotify_mark,
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fsn_mark);
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assert_spin_locked(&fsn_mark->lock);
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for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
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new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
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if (fsn_mark->mask == new_mask)
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return;
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fsn_mark->mask = new_mask;
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fsnotify_recalc_mask(fsn_mark->connector);
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}
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/*
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* Mains fsnotify call where events are delivered to dnotify.
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* Find the dnotify mark on the relevant inode, run the list of dnotify structs
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* on that mark and determine which of them has expressed interest in receiving
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* events of this type. When found send the correct process and signal and
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* destroy the dnotify struct if it was not registered to receive multiple
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* events.
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*/
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static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
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struct inode *inode, struct inode *dir,
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const struct qstr *name, u32 cookie)
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{
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struct dnotify_mark *dn_mark;
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struct dnotify_struct *dn;
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struct dnotify_struct **prev;
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struct fown_struct *fown;
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__u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
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/* not a dir, dnotify doesn't care */
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if (!dir && !(mask & FS_ISDIR))
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return 0;
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dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
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spin_lock(&inode_mark->lock);
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prev = &dn_mark->dn;
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while ((dn = *prev) != NULL) {
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if ((dn->dn_mask & test_mask) == 0) {
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prev = &dn->dn_next;
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continue;
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}
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fown = &dn->dn_filp->f_owner;
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send_sigio(fown, dn->dn_fd, POLL_MSG);
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if (dn->dn_mask & FS_DN_MULTISHOT)
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prev = &dn->dn_next;
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else {
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*prev = dn->dn_next;
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kmem_cache_free(dnotify_struct_cache, dn);
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dnotify_recalc_inode_mask(inode_mark);
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}
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}
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spin_unlock(&inode_mark->lock);
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return 0;
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}
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static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
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{
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struct dnotify_mark *dn_mark = container_of(fsn_mark,
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struct dnotify_mark,
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fsn_mark);
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BUG_ON(dn_mark->dn);
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kmem_cache_free(dnotify_mark_cache, dn_mark);
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}
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static const struct fsnotify_ops dnotify_fsnotify_ops = {
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.handle_inode_event = dnotify_handle_event,
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.free_mark = dnotify_free_mark,
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};
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/*
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* Called every time a file is closed. Looks first for a dnotify mark on the
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* inode. If one is found run all of the ->dn structures attached to that
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* mark for one relevant to this process closing the file and remove that
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* dnotify_struct. If that was the last dnotify_struct also remove the
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* fsnotify_mark.
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*/
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void dnotify_flush(struct file *filp, fl_owner_t id)
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{
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struct fsnotify_mark *fsn_mark;
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struct dnotify_mark *dn_mark;
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struct dnotify_struct *dn;
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struct dnotify_struct **prev;
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struct inode *inode;
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bool free = false;
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inode = file_inode(filp);
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if (!S_ISDIR(inode->i_mode))
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return;
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fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
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if (!fsn_mark)
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return;
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dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
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mutex_lock(&dnotify_group->mark_mutex);
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spin_lock(&fsn_mark->lock);
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prev = &dn_mark->dn;
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while ((dn = *prev) != NULL) {
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if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
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*prev = dn->dn_next;
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kmem_cache_free(dnotify_struct_cache, dn);
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dnotify_recalc_inode_mask(fsn_mark);
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break;
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}
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prev = &dn->dn_next;
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}
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spin_unlock(&fsn_mark->lock);
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/* nothing else could have found us thanks to the dnotify_groups
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mark_mutex */
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if (dn_mark->dn == NULL) {
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fsnotify_detach_mark(fsn_mark);
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free = true;
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}
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mutex_unlock(&dnotify_group->mark_mutex);
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if (free)
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fsnotify_free_mark(fsn_mark);
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fsnotify_put_mark(fsn_mark);
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}
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/* this conversion is done only at watch creation */
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static __u32 convert_arg(unsigned long arg)
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{
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__u32 new_mask = FS_EVENT_ON_CHILD;
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if (arg & DN_MULTISHOT)
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new_mask |= FS_DN_MULTISHOT;
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if (arg & DN_DELETE)
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new_mask |= (FS_DELETE | FS_MOVED_FROM);
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if (arg & DN_MODIFY)
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new_mask |= FS_MODIFY;
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if (arg & DN_ACCESS)
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new_mask |= FS_ACCESS;
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if (arg & DN_ATTRIB)
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new_mask |= FS_ATTRIB;
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if (arg & DN_RENAME)
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new_mask |= FS_DN_RENAME;
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if (arg & DN_CREATE)
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new_mask |= (FS_CREATE | FS_MOVED_TO);
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return new_mask;
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}
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/*
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* If multiple processes watch the same inode with dnotify there is only one
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* dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
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* onto that mark. This function either attaches the new dnotify_struct onto
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* that list, or it |= the mask onto an existing dnofiy_struct.
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*/
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static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
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fl_owner_t id, int fd, struct file *filp, __u32 mask)
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{
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struct dnotify_struct *odn;
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odn = dn_mark->dn;
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while (odn != NULL) {
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/* adding more events to existing dnofiy_struct? */
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if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
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odn->dn_fd = fd;
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odn->dn_mask |= mask;
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return -EEXIST;
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}
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odn = odn->dn_next;
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}
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dn->dn_mask = mask;
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dn->dn_fd = fd;
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dn->dn_filp = filp;
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dn->dn_owner = id;
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dn->dn_next = dn_mark->dn;
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dn_mark->dn = dn;
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return 0;
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}
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/*
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* When a process calls fcntl to attach a dnotify watch to a directory it ends
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* up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
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* attached to the fsnotify_mark.
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*/
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int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
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{
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struct dnotify_mark *new_dn_mark, *dn_mark;
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struct fsnotify_mark *new_fsn_mark, *fsn_mark;
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struct dnotify_struct *dn;
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struct inode *inode;
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fl_owner_t id = current->files;
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struct file *f;
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int destroy = 0, error = 0;
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__u32 mask;
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/* we use these to tell if we need to kfree */
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new_fsn_mark = NULL;
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dn = NULL;
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if (!dir_notify_enable) {
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error = -EINVAL;
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goto out_err;
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}
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/* a 0 mask means we are explicitly removing the watch */
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if ((arg & ~DN_MULTISHOT) == 0) {
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dnotify_flush(filp, id);
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error = 0;
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goto out_err;
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}
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/* dnotify only works on directories */
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inode = file_inode(filp);
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if (!S_ISDIR(inode->i_mode)) {
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error = -ENOTDIR;
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goto out_err;
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}
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/*
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* convert the userspace DN_* "arg" to the internal FS_*
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* defined in fsnotify
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*/
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mask = convert_arg(arg);
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error = security_path_notify(&filp->f_path, mask,
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FSNOTIFY_OBJ_TYPE_INODE);
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if (error)
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goto out_err;
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/* expect most fcntl to add new rather than augment old */
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dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
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if (!dn) {
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error = -ENOMEM;
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goto out_err;
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}
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/* new fsnotify mark, we expect most fcntl calls to add a new mark */
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new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
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if (!new_dn_mark) {
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error = -ENOMEM;
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goto out_err;
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}
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/* set up the new_fsn_mark and new_dn_mark */
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new_fsn_mark = &new_dn_mark->fsn_mark;
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fsnotify_init_mark(new_fsn_mark, dnotify_group);
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new_fsn_mark->mask = mask;
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new_dn_mark->dn = NULL;
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/* this is needed to prevent the fcntl/close race described below */
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mutex_lock(&dnotify_group->mark_mutex);
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/* add the new_fsn_mark or find an old one. */
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fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
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if (fsn_mark) {
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dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
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spin_lock(&fsn_mark->lock);
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} else {
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error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
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if (error) {
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mutex_unlock(&dnotify_group->mark_mutex);
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goto out_err;
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}
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spin_lock(&new_fsn_mark->lock);
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fsn_mark = new_fsn_mark;
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dn_mark = new_dn_mark;
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/* we used new_fsn_mark, so don't free it */
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new_fsn_mark = NULL;
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}
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rcu_read_lock();
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f = fcheck(fd);
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rcu_read_unlock();
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/* if (f != filp) means that we lost a race and another task/thread
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* actually closed the fd we are still playing with before we grabbed
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* the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the
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* fd is the only time we clean up the marks we need to get our mark
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* off the list. */
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if (f != filp) {
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/* if we added ourselves, shoot ourselves, it's possible that
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* the flush actually did shoot this fsn_mark. That's fine too
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* since multiple calls to destroy_mark is perfectly safe, if
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* we found a dn_mark already attached to the inode, just sod
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* off silently as the flush at close time dealt with it.
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*/
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if (dn_mark == new_dn_mark)
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destroy = 1;
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error = 0;
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goto out;
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}
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__f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
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error = attach_dn(dn, dn_mark, id, fd, filp, mask);
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/* !error means that we attached the dn to the dn_mark, so don't free it */
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if (!error)
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dn = NULL;
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/* -EEXIST means that we didn't add this new dn and used an old one.
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* that isn't an error (and the unused dn should be freed) */
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else if (error == -EEXIST)
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error = 0;
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dnotify_recalc_inode_mask(fsn_mark);
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out:
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spin_unlock(&fsn_mark->lock);
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if (destroy)
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fsnotify_detach_mark(fsn_mark);
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mutex_unlock(&dnotify_group->mark_mutex);
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if (destroy)
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fsnotify_free_mark(fsn_mark);
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fsnotify_put_mark(fsn_mark);
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out_err:
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if (new_fsn_mark)
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fsnotify_put_mark(new_fsn_mark);
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if (dn)
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kmem_cache_free(dnotify_struct_cache, dn);
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return error;
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}
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static int __init dnotify_init(void)
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{
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dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
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SLAB_PANIC|SLAB_ACCOUNT);
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dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
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dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
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if (IS_ERR(dnotify_group))
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panic("unable to allocate fsnotify group for dnotify\n");
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return 0;
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}
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module_init(dnotify_init)
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