// SPDX-License-Identifier: GPL-2.0-or-later
/* audit_watch.c -- watching inodes
 *
 * Copyright 2003-2009 Red Hat, Inc.
 * Copyright 2005 Hewlett-Packard Development Company, L.P.
 * Copyright 2005 IBM Corporation
 */

#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/audit.h>
#include <linux/kthread.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <linux/fsnotify_backend.h>
#include <linux/namei.h>
#include <linux/netlink.h>
#include <linux/refcount.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/security.h>
#include "audit.h"

/*
 * Reference counting:
 *
 * audit_parent: lifetime is from audit_init_parent() to receipt of an FS_IGNORED
 *      event.  Each audit_watch holds a reference to its associated parent.
 *
 * audit_watch: if added to lists, lifetime is from audit_init_watch() to
 *      audit_remove_watch().  Additionally, an audit_watch may exist
 *      temporarily to assist in searching existing filter data.  Each
 *      audit_krule holds a reference to its associated watch.
 */

struct audit_watch {
        refcount_t              count;  /* reference count */
        dev_t                   dev;    /* associated superblock device */
        char                    *path;  /* insertion path */
        unsigned long           ino;    /* associated inode number */
        struct audit_parent     *parent; /* associated parent */
        struct list_head        wlist;  /* entry in parent->watches list */
        struct list_head        rules;  /* anchor for krule->rlist */
};

struct audit_parent {
        struct list_head        watches; /* anchor for audit_watch->wlist */
        struct fsnotify_mark mark; /* fsnotify mark on the inode */
};

/* fsnotify handle. */
static struct fsnotify_group *audit_watch_group;

/* fsnotify events we care about. */
#define AUDIT_FS_WATCH (FS_MOVE | FS_CREATE | FS_DELETE | FS_DELETE_SELF |\
                        FS_MOVE_SELF | FS_UNMOUNT)

static void audit_free_parent(struct audit_parent *parent)
{
        WARN_ON(!list_empty(&parent->watches));
        kfree(parent);
}

static void audit_watch_free_mark(struct fsnotify_mark *entry)
{
        struct audit_parent *parent;

        parent = container_of(entry, struct audit_parent, mark);
        audit_free_parent(parent);
}

static void audit_get_parent(struct audit_parent *parent)
{
        if (likely(parent))
                fsnotify_get_mark(&parent->mark);
}

static void audit_put_parent(struct audit_parent *parent)
{
        if (likely(parent))
                fsnotify_put_mark(&parent->mark);
}

/*
 * Find and return the audit_parent on the given inode.  If found a reference
 * is taken on this parent.
 */
static inline struct audit_parent *audit_find_parent(struct inode *inode)
{
        struct audit_parent *parent = NULL;
        struct fsnotify_mark *entry;

        entry = fsnotify_find_mark(&inode->i_fsnotify_marks, audit_watch_group);
        if (entry)
                parent = container_of(entry, struct audit_parent, mark);

        return parent;
}

void audit_get_watch(struct audit_watch *watch)
{
        refcount_inc(&watch->count);
}

void audit_put_watch(struct audit_watch *watch)
{
        if (refcount_dec_and_test(&watch->count)) {
                WARN_ON(watch->parent);
                WARN_ON(!list_empty(&watch->rules));
                kfree(watch->path);
                kfree(watch);
        }
}

static void audit_remove_watch(struct audit_watch *watch)
{
        list_del(&watch->wlist);
        audit_put_parent(watch->parent);
        watch->parent = NULL;
        audit_put_watch(watch); /* match initial get */
}

char *audit_watch_path(struct audit_watch *watch)
{
        return watch->path;
}

int audit_watch_compare(struct audit_watch *watch, unsigned long ino, dev_t dev)
{
        return (watch->ino != AUDIT_INO_UNSET) &&
                (watch->ino == ino) &&
                (watch->dev == dev);
}

/* Initialize a parent watch entry. */
static struct audit_parent *audit_init_parent(struct path *path)
{
        struct inode *inode = d_backing_inode(path->dentry);
        struct audit_parent *parent;
        int ret;

        parent = kzalloc(sizeof(*parent), GFP_KERNEL);
        if (unlikely(!parent))
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&parent->watches);

        fsnotify_init_mark(&parent->mark, audit_watch_group);
        parent->mark.mask = AUDIT_FS_WATCH;
        ret = fsnotify_add_inode_mark(&parent->mark, inode, 0);
        if (ret < 0) {
                audit_free_parent(parent);
                return ERR_PTR(ret);
        }

        return parent;
}

/* Initialize a watch entry. */
static struct audit_watch *audit_init_watch(char *path)
{
        struct audit_watch *watch;

        watch = kzalloc(sizeof(*watch), GFP_KERNEL);
        if (unlikely(!watch))
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&watch->rules);
        refcount_set(&watch->count, 1);
        watch->path = path;
        watch->dev = AUDIT_DEV_UNSET;
        watch->ino = AUDIT_INO_UNSET;

        return watch;
}

/* Translate a watch string to kernel representation. */
int audit_to_watch(struct audit_krule *krule, char *path, int len, u32 op)
{
        struct audit_watch *watch;

        if (!audit_watch_group)
                return -EOPNOTSUPP;

        if (path[0] != '/' || path[len-1] == '/' ||
            krule->listnr != AUDIT_FILTER_EXIT ||
            op != Audit_equal ||
            krule->inode_f || krule->watch || krule->tree)
                return -EINVAL;

        watch = audit_init_watch(path);
        if (IS_ERR(watch))
                return PTR_ERR(watch);

        krule->watch = watch;

        return 0;
}

/* Duplicate the given audit watch.  The new watch's rules list is initialized
 * to an empty list and wlist is undefined. */
static struct audit_watch *audit_dupe_watch(struct audit_watch *old)
{
        char *path;
        struct audit_watch *new;

        path = kstrdup(old->path, GFP_KERNEL);
        if (unlikely(!path))
                return ERR_PTR(-ENOMEM);

        new = audit_init_watch(path);
        if (IS_ERR(new)) {
                kfree(path);
                goto out;
        }

        new->dev = old->dev;
        new->ino = old->ino;
        audit_get_parent(old->parent);
        new->parent = old->parent;

out:
        return new;
}

static void audit_watch_log_rule_change(struct audit_krule *r, struct audit_watch *w, char *op)
{
        struct audit_buffer *ab;

        if (!audit_enabled)
                return;
        ab = audit_log_start(audit_context(), GFP_NOFS, AUDIT_CONFIG_CHANGE);
        if (!ab)
                return;
        audit_log_session_info(ab);
        audit_log_format(ab, "op=%s path=", op);
        audit_log_untrustedstring(ab, w->path);
        audit_log_key(ab, r->filterkey);
        audit_log_format(ab, " list=%d res=1", r->listnr);
        audit_log_end(ab);
}

/* Update inode info in audit rules based on filesystem event. */
static void audit_update_watch(struct audit_parent *parent,
                               const struct qstr *dname, dev_t dev,
                               unsigned long ino, unsigned invalidating)
{
        struct audit_watch *owatch, *nwatch, *nextw;
        struct audit_krule *r, *nextr;
        struct audit_entry *oentry, *nentry;

        mutex_lock(&audit_filter_mutex);
        /* Run all of the watches on this parent looking for the one that
         * matches the given dname */
        list_for_each_entry_safe(owatch, nextw, &parent->watches, wlist) {
                if (audit_compare_dname_path(dname, owatch->path,
                                             AUDIT_NAME_FULL))
                        continue;

                /* If the update involves invalidating rules, do the inode-based
                 * filtering now, so we don't omit records. */
                if (invalidating && !audit_dummy_context())
                        audit_filter_inodes(current, audit_context());

                /* updating ino will likely change which audit_hash_list we
                 * are on so we need a new watch for the new list */
                nwatch = audit_dupe_watch(owatch);
                if (IS_ERR(nwatch)) {
                        mutex_unlock(&audit_filter_mutex);
                        audit_panic("error updating watch, skipping");
                        return;
                }
                nwatch->dev = dev;
                nwatch->ino = ino;

                list_for_each_entry_safe(r, nextr, &owatch->rules, rlist) {

                        oentry = container_of(r, struct audit_entry, rule);
                        list_del(&oentry->rule.rlist);
                        list_del_rcu(&oentry->list);

                        nentry = audit_dupe_rule(&oentry->rule);
                        if (IS_ERR(nentry)) {
                                list_del(&oentry->rule.list);
                                audit_panic("error updating watch, removing");
                        } else {
                                int h = audit_hash_ino((u32)ino);

                                /*
                                 * nentry->rule.watch == oentry->rule.watch so
                                 * we must drop that reference and set it to our
                                 * new watch.
                                 */
                                audit_put_watch(nentry->rule.watch);
                                audit_get_watch(nwatch);
                                nentry->rule.watch = nwatch;
                                list_add(&nentry->rule.rlist, &nwatch->rules);
                                list_add_rcu(&nentry->list, &audit_inode_hash[h]);
                                list_replace(&oentry->rule.list,
                                             &nentry->rule.list);
                        }
                        if (oentry->rule.exe)
                                audit_remove_mark(oentry->rule.exe);

                        call_rcu(&oentry->rcu, audit_free_rule_rcu);
                }

                audit_remove_watch(owatch);
                goto add_watch_to_parent; /* event applies to a single watch */
        }
        mutex_unlock(&audit_filter_mutex);
        return;

add_watch_to_parent:
        list_add(&nwatch->wlist, &parent->watches);
        mutex_unlock(&audit_filter_mutex);
        return;
}

/* Remove all watches & rules associated with a parent that is going away. */
static void audit_remove_parent_watches(struct audit_parent *parent)
{
        struct audit_watch *w, *nextw;
        struct audit_krule *r, *nextr;
        struct audit_entry *e;

        mutex_lock(&audit_filter_mutex);
        list_for_each_entry_safe(w, nextw, &parent->watches, wlist) {
                list_for_each_entry_safe(r, nextr, &w->rules, rlist) {
                        e = container_of(r, struct audit_entry, rule);
                        audit_watch_log_rule_change(r, w, "remove_rule");
                        if (e->rule.exe)
                                audit_remove_mark(e->rule.exe);
                        list_del(&r->rlist);
                        list_del(&r->list);
                        list_del_rcu(&e->list);
                        call_rcu(&e->rcu, audit_free_rule_rcu);
                }
                audit_remove_watch(w);
        }
        mutex_unlock(&audit_filter_mutex);

        fsnotify_destroy_mark(&parent->mark, audit_watch_group);
}

/* Get path information necessary for adding watches. */
static int audit_get_nd(struct audit_watch *watch, struct path *parent)
{
        struct dentry *d = kern_path_locked(watch->path, parent);
        if (IS_ERR(d))
                return PTR_ERR(d);
        if (d_is_positive(d)) {
                /* update watch filter fields */
                watch->dev = d->d_sb->s_dev;
                watch->ino = d_backing_inode(d)->i_ino;
        }
        inode_unlock(d_backing_inode(parent->dentry));
        dput(d);
        return 0;
}

/* Associate the given rule with an existing parent.
 * Caller must hold audit_filter_mutex. */
static void audit_add_to_parent(struct audit_krule *krule,
                                struct audit_parent *parent)
{
        struct audit_watch *w, *watch = krule->watch;
        int watch_found = 0;

        BUG_ON(!mutex_is_locked(&audit_filter_mutex));

        list_for_each_entry(w, &parent->watches, wlist) {
                if (strcmp(watch->path, w->path))
                        continue;

                watch_found = 1;

                /* put krule's ref to temporary watch */
                audit_put_watch(watch);

                audit_get_watch(w);
                krule->watch = watch = w;

                audit_put_parent(parent);
                break;
        }

        if (!watch_found) {
                watch->parent = parent;

                audit_get_watch(watch);
                list_add(&watch->wlist, &parent->watches);
        }
        list_add(&krule->rlist, &watch->rules);
}

/* Find a matching watch entry, or add this one.
 * Caller must hold audit_filter_mutex. */
int audit_add_watch(struct audit_krule *krule, struct list_head **list)
{
        struct audit_watch *watch = krule->watch;
        struct audit_parent *parent;
        struct path parent_path;
        int h, ret = 0;

        /*
         * When we will be calling audit_add_to_parent, krule->watch might have
         * been updated and watch might have been freed.
         * So we need to keep a reference of watch.
         */
        audit_get_watch(watch);

        mutex_unlock(&audit_filter_mutex);

        /* Avoid calling path_lookup under audit_filter_mutex. */
        ret = audit_get_nd(watch, &parent_path);

        /* caller expects mutex locked */
        mutex_lock(&audit_filter_mutex);

        if (ret) {
                audit_put_watch(watch);
                return ret;
        }

        /* either find an old parent or attach a new one */
        parent = audit_find_parent(d_backing_inode(parent_path.dentry));
        if (!parent) {
                parent = audit_init_parent(&parent_path);
                if (IS_ERR(parent)) {
                        ret = PTR_ERR(parent);
                        goto error;
                }
        }

        audit_add_to_parent(krule, parent);

        h = audit_hash_ino((u32)watch->ino);
        *list = &audit_inode_hash[h];
error:
        path_put(&parent_path);
        audit_put_watch(watch);
        return ret;
}

void audit_remove_watch_rule(struct audit_krule *krule)
{
        struct audit_watch *watch = krule->watch;
        struct audit_parent *parent = watch->parent;

        list_del(&krule->rlist);

        if (list_empty(&watch->rules)) {
                /*
                 * audit_remove_watch() drops our reference to 'parent' which
                 * can get freed. Grab our own reference to be safe.
                 */
                audit_get_parent(parent);
                audit_remove_watch(watch);
                if (list_empty(&parent->watches))
                        fsnotify_destroy_mark(&parent->mark, audit_watch_group);
                audit_put_parent(parent);
        }
}

/* Update watch data in audit rules based on fsnotify events. */
static int audit_watch_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
                                    struct inode *inode, struct inode *dir,
                                    const struct qstr *dname)
{
        struct audit_parent *parent;

        parent = container_of(inode_mark, struct audit_parent, mark);

        if (WARN_ON_ONCE(inode_mark->group != audit_watch_group) ||
            WARN_ON_ONCE(!inode))
                return 0;

        if (mask & (FS_CREATE|FS_MOVED_TO) && inode)
                audit_update_watch(parent, dname, inode->i_sb->s_dev, inode->i_ino, 0);
        else if (mask & (FS_DELETE|FS_MOVED_FROM))
                audit_update_watch(parent, dname, AUDIT_DEV_UNSET, AUDIT_INO_UNSET, 1);
        else if (mask & (FS_DELETE_SELF|FS_UNMOUNT|FS_MOVE_SELF))
                audit_remove_parent_watches(parent);

        return 0;
}

static const struct fsnotify_ops audit_watch_fsnotify_ops = {
        .handle_inode_event =   audit_watch_handle_event,
        .free_mark =            audit_watch_free_mark,
};

static int __init audit_watch_init(void)
{
        audit_watch_group = fsnotify_alloc_group(&audit_watch_fsnotify_ops);
        if (IS_ERR(audit_watch_group)) {
                audit_watch_group = NULL;
                audit_panic("cannot create audit fsnotify group");
        }
        return 0;
}
device_initcall(audit_watch_init);

int audit_dupe_exe(struct audit_krule *new, struct audit_krule *old)
{
        struct audit_fsnotify_mark *audit_mark;
        char *pathname;

        pathname = kstrdup(audit_mark_path(old->exe), GFP_KERNEL);
        if (!pathname)
                return -ENOMEM;

        audit_mark = audit_alloc_mark(new, pathname, strlen(pathname));
        if (IS_ERR(audit_mark)) {
                kfree(pathname);
                return PTR_ERR(audit_mark);
        }
        new->exe = audit_mark;

        return 0;
}

int audit_exe_compare(struct task_struct *tsk, struct audit_fsnotify_mark *mark)
{
        struct file *exe_file;
        unsigned long ino;
        dev_t dev;

        exe_file = get_task_exe_file(tsk);
        if (!exe_file)
                return 0;
        ino = file_inode(exe_file)->i_ino;
        dev = file_inode(exe_file)->i_sb->s_dev;
        fput(exe_file);
        return audit_mark_compare(mark, ino, dev);
}