fanotify: merge duplicate events on parent and child

[linux/fpc-iii.git] / fs / notify / fanotify / fanotify.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/sched/signal.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <linux/audit.h>
#include <linux/sched/mm.h>
#include <linux/statfs.h>

#include "fanotify.h"

static bool should_merge(struct fsnotify_event *old_fsn,
                         struct fsnotify_event *new_fsn)
{
        struct fanotify_event *old, *new;

        pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
        old = FANOTIFY_E(old_fsn);
        new = FANOTIFY_E(new_fsn);

        if (old_fsn->objectid != new_fsn->objectid || old->pid != new->pid ||
            old->fh_type != new->fh_type || old->fh_len != new->fh_len)
                return false;

        if (fanotify_event_has_path(old)) {
                return old->path.mnt == new->path.mnt &&
                        old->path.dentry == new->path.dentry;
        } else if (fanotify_event_has_fid(old)) {
                /*
                 * We want to merge many dirent events in the same dir (i.e.
                 * creates/unlinks/renames), but we do not want to merge dirent
                 * events referring to subdirs with dirent events referring to
                 * non subdirs, otherwise, user won't be able to tell from a
                 * mask FAN_CREATE|FAN_DELETE|FAN_ONDIR if it describes mkdir+
                 * unlink pair or rmdir+create pair of events.
                 */
                return (old->mask & FS_ISDIR) == (new->mask & FS_ISDIR) &&
                        fanotify_fid_equal(&old->fid, &new->fid, old->fh_len);
        }

        /* Do not merge events if we failed to encode fid */
        return false;
}

/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
        struct fsnotify_event *test_event;
        struct fanotify_event *new;

        pr_debug("%s: list=%p event=%p\n", __func__, list, event);
        new = FANOTIFY_E(event);

        /*
         * Don't merge a permission event with any other event so that we know
         * the event structure we have created in fanotify_handle_event() is the
         * one we should check for permission response.
         */
        if (fanotify_is_perm_event(new->mask))
                return 0;

        list_for_each_entry_reverse(test_event, list, list) {
                if (should_merge(test_event, event)) {
                        FANOTIFY_E(test_event)->mask |= new->mask;
                        return 1;
                }
        }

        return 0;
}

/*
 * Wait for response to permission event. The function also takes care of
 * freeing the permission event (or offloads that in case the wait is canceled
 * by a signal). The function returns 0 in case access got allowed by userspace,
 * -EPERM in case userspace disallowed the access, and -ERESTARTSYS in case
 * the wait got interrupted by a signal.
 */
static int fanotify_get_response(struct fsnotify_group *group,
                                 struct fanotify_perm_event *event,
                                 struct fsnotify_iter_info *iter_info)
{
        int ret;

        pr_debug("%s: group=%p event=%p\n", __func__, group, event);

        ret = wait_event_killable(group->fanotify_data.access_waitq,
                                  event->state == FAN_EVENT_ANSWERED);
        /* Signal pending? */
        if (ret < 0) {
                spin_lock(&group->notification_lock);
                /* Event reported to userspace and no answer yet? */
                if (event->state == FAN_EVENT_REPORTED) {
                        /* Event will get freed once userspace answers to it */
                        event->state = FAN_EVENT_CANCELED;
                        spin_unlock(&group->notification_lock);
                        return ret;
                }
                /* Event not yet reported? Just remove it. */
                if (event->state == FAN_EVENT_INIT)
                        fsnotify_remove_queued_event(group, &event->fae.fse);
                /*
                 * Event may be also answered in case signal delivery raced
                 * with wakeup. In that case we have nothing to do besides
                 * freeing the event and reporting error.
                 */
                spin_unlock(&group->notification_lock);
                goto out;
        }

        /* userspace responded, convert to something usable */
        switch (event->response & ~FAN_AUDIT) {
        case FAN_ALLOW:
                ret = 0;
                break;
        case FAN_DENY:
        default:
                ret = -EPERM;
        }

        /* Check if the response should be audited */
        if (event->response & FAN_AUDIT)
                audit_fanotify(event->response & ~FAN_AUDIT);

        pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
                 group, event, ret);
out:
        fsnotify_destroy_event(group, &event->fae.fse);

        return ret;
}

/*
 * This function returns a mask for an event that only contains the flags
 * that have been specifically requested by the user. Flags that may have
 * been included within the event mask, but have not been explicitly
 * requested by the user, will not be present in the returned mask.
 */
static u32 fanotify_group_event_mask(struct fsnotify_group *group,
                                     struct fsnotify_iter_info *iter_info,
                                     u32 event_mask, const void *data,
                                     int data_type)
{
        __u32 marks_mask = 0, marks_ignored_mask = 0;
        __u32 test_mask, user_mask = FANOTIFY_OUTGOING_EVENTS;
        const struct path *path = data;
        struct fsnotify_mark *mark;
        int type;

        pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
                 __func__, iter_info->report_mask, event_mask, data, data_type);

        if (!FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                /* Do we have path to open a file descriptor? */
                if (data_type != FSNOTIFY_EVENT_PATH)
                        return 0;
                /* Path type events are only relevant for files and dirs */
                if (!d_is_reg(path->dentry) && !d_can_lookup(path->dentry))
                        return 0;
        }

        fsnotify_foreach_obj_type(type) {
                if (!fsnotify_iter_should_report_type(iter_info, type))
                        continue;
                mark = iter_info->marks[type];
                /*
                 * If the event is for a child and this mark doesn't care about
                 * events on a child, don't send it!
                 */
                if (event_mask & FS_EVENT_ON_CHILD &&
                    (type != FSNOTIFY_OBJ_TYPE_INODE ||
                     !(mark->mask & FS_EVENT_ON_CHILD)))
                        continue;

                marks_mask |= mark->mask;
                marks_ignored_mask |= mark->ignored_mask;
        }

        test_mask = event_mask & marks_mask & ~marks_ignored_mask;

        /*
         * dirent modification events (create/delete/move) do not carry the
         * child entry name/inode information. Instead, we report FAN_ONDIR
         * for mkdir/rmdir so user can differentiate them from creat/unlink.
         *
         * For backward compatibility and consistency, do not report FAN_ONDIR
         * to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
         * to user in FAN_REPORT_FID mode for all event types.
         */
        if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                /* Do not report FAN_ONDIR without any event */
                if (!(test_mask & ~FAN_ONDIR))
                        return 0;
        } else {
                user_mask &= ~FAN_ONDIR;
        }

        if (event_mask & FS_ISDIR &&
            !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
                return 0;

        return test_mask & user_mask;
}

static int fanotify_encode_fid(struct fanotify_event *event,
                               struct inode *inode, gfp_t gfp,
                               __kernel_fsid_t *fsid)
{
        struct fanotify_fid *fid = &event->fid;
        int dwords, bytes = 0;
        int err, type;

        fid->ext_fh = NULL;
        dwords = 0;
        err = -ENOENT;
        type = exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
        if (!dwords)
                goto out_err;

        bytes = dwords << 2;
        if (bytes > FANOTIFY_INLINE_FH_LEN) {
                /* Treat failure to allocate fh as failure to allocate event */
                err = -ENOMEM;
                fid->ext_fh = kmalloc(bytes, gfp);
                if (!fid->ext_fh)
                        goto out_err;
        }

        type = exportfs_encode_inode_fh(inode, fanotify_fid_fh(fid, bytes),
                                        &dwords, NULL);
        err = -EINVAL;
        if (!type || type == FILEID_INVALID || bytes != dwords << 2)
                goto out_err;

        fid->fsid = *fsid;
        event->fh_len = bytes;

        return type;

out_err:
        pr_warn_ratelimited("fanotify: failed to encode fid (fsid=%x.%x, "
                            "type=%d, bytes=%d, err=%i)\n",
                            fsid->val[0], fsid->val[1], type, bytes, err);
        kfree(fid->ext_fh);
        fid->ext_fh = NULL;
        event->fh_len = 0;

        return FILEID_INVALID;
}

/*
 * The inode to use as identifier when reporting fid depends on the event.
 * Report the modified directory inode on dirent modification events.
 * Report the "victim" inode otherwise.
 * For example:
 * FS_ATTRIB reports the child inode even if reported on a watched parent.
 * FS_CREATE reports the modified dir inode and not the created inode.
 */
static struct inode *fanotify_fid_inode(struct inode *to_tell, u32 event_mask,
                                        const void *data, int data_type)
{
        if (event_mask & ALL_FSNOTIFY_DIRENT_EVENTS)
                return to_tell;
        else if (data_type == FSNOTIFY_EVENT_INODE)
                return (struct inode *)data;
        else if (data_type == FSNOTIFY_EVENT_PATH)
                return d_inode(((struct path *)data)->dentry);
        return NULL;
}

struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
                                            struct inode *inode, u32 mask,
                                            const void *data, int data_type,
                                            __kernel_fsid_t *fsid)
{
        struct fanotify_event *event = NULL;
        gfp_t gfp = GFP_KERNEL_ACCOUNT;
        struct inode *id = fanotify_fid_inode(inode, mask, data, data_type);

        /*
         * For queues with unlimited length lost events are not expected and
         * can possibly have security implications. Avoid losing events when
         * memory is short. For the limited size queues, avoid OOM killer in the
         * target monitoring memcg as it may have security repercussion.
         */
        if (group->max_events == UINT_MAX)
                gfp |= __GFP_NOFAIL;
        else
                gfp |= __GFP_RETRY_MAYFAIL;

        /* Whoever is interested in the event, pays for the allocation. */
        memalloc_use_memcg(group->memcg);

        if (fanotify_is_perm_event(mask)) {
                struct fanotify_perm_event *pevent;

                pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
                if (!pevent)
                        goto out;
                event = &pevent->fae;
                pevent->response = 0;
                pevent->state = FAN_EVENT_INIT;
                goto init;
        }
        event = kmem_cache_alloc(fanotify_event_cachep, gfp);
        if (!event)
                goto out;
init: __maybe_unused
        /*
         * Use the victim inode instead of the watching inode as the id for
         * event queue, so event reported on parent is merged with event
         * reported on child when both directory and child watches exist.
         */
        fsnotify_init_event(&event->fse, (unsigned long)id);
        event->mask = mask;
        if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
                event->pid = get_pid(task_pid(current));
        else
                event->pid = get_pid(task_tgid(current));
        event->fh_len = 0;
        if (id && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                /* Report the event without a file identifier on encode error */
                event->fh_type = fanotify_encode_fid(event, id, gfp, fsid);
        } else if (data_type == FSNOTIFY_EVENT_PATH) {
                event->fh_type = FILEID_ROOT;
                event->path = *((struct path *)data);
                path_get(&event->path);
        } else {
                event->fh_type = FILEID_INVALID;
                event->path.mnt = NULL;
                event->path.dentry = NULL;
        }
out:
        memalloc_unuse_memcg();
        return event;
}

/*
 * Get cached fsid of the filesystem containing the object from any connector.
 * All connectors are supposed to have the same fsid, but we do not verify that
 * here.
 */
static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
{
        int type;
        __kernel_fsid_t fsid = {};

        fsnotify_foreach_obj_type(type) {
                struct fsnotify_mark_connector *conn;

                if (!fsnotify_iter_should_report_type(iter_info, type))
                        continue;

                conn = READ_ONCE(iter_info->marks[type]->connector);
                /* Mark is just getting destroyed or created? */
                if (!conn)
                        continue;
                if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID))
                        continue;
                /* Pairs with smp_wmb() in fsnotify_add_mark_list() */
                smp_rmb();
                fsid = conn->fsid;
                if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
                        continue;
                return fsid;
        }

        return fsid;
}

static int fanotify_handle_event(struct fsnotify_group *group,
                                 struct inode *inode,
                                 u32 mask, const void *data, int data_type,
                                 const struct qstr *file_name, u32 cookie,
                                 struct fsnotify_iter_info *iter_info)
{
        int ret = 0;
        struct fanotify_event *event;
        struct fsnotify_event *fsn_event;
        __kernel_fsid_t fsid = {};

        BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
        BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
        BUILD_BUG_ON(FAN_ATTRIB != FS_ATTRIB);
        BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
        BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
        BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
        BUILD_BUG_ON(FAN_MOVED_TO != FS_MOVED_TO);
        BUILD_BUG_ON(FAN_MOVED_FROM != FS_MOVED_FROM);
        BUILD_BUG_ON(FAN_CREATE != FS_CREATE);
        BUILD_BUG_ON(FAN_DELETE != FS_DELETE);
        BUILD_BUG_ON(FAN_DELETE_SELF != FS_DELETE_SELF);
        BUILD_BUG_ON(FAN_MOVE_SELF != FS_MOVE_SELF);
        BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
        BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
        BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
        BUILD_BUG_ON(FAN_OPEN_EXEC != FS_OPEN_EXEC);
        BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);

        BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 19);

        mask = fanotify_group_event_mask(group, iter_info, mask, data,
                                         data_type);
        if (!mask)
                return 0;

        pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
                 mask);

        if (fanotify_is_perm_event(mask)) {
                /*
                 * fsnotify_prepare_user_wait() fails if we race with mark
                 * deletion.  Just let the operation pass in that case.
                 */
                if (!fsnotify_prepare_user_wait(iter_info))
                        return 0;
        }

        if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                fsid = fanotify_get_fsid(iter_info);
                /* Racing with mark destruction or creation? */
                if (!fsid.val[0] && !fsid.val[1])
                        return 0;
        }

        event = fanotify_alloc_event(group, inode, mask, data, data_type,
                                     &fsid);
        ret = -ENOMEM;
        if (unlikely(!event)) {
                /*
                 * We don't queue overflow events for permission events as
                 * there the access is denied and so no event is in fact lost.
                 */
                if (!fanotify_is_perm_event(mask))
                        fsnotify_queue_overflow(group);
                goto finish;
        }

        fsn_event = &event->fse;
        ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
        if (ret) {
                /* Permission events shouldn't be merged */
                BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
                /* Our event wasn't used in the end. Free it. */
                fsnotify_destroy_event(group, fsn_event);

                ret = 0;
        } else if (fanotify_is_perm_event(mask)) {
                ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
                                            iter_info);
        }
finish:
        if (fanotify_is_perm_event(mask))
                fsnotify_finish_user_wait(iter_info);

        return ret;
}

static void fanotify_free_group_priv(struct fsnotify_group *group)
{
        struct user_struct *user;

        user = group->fanotify_data.user;
        atomic_dec(&user->fanotify_listeners);
        free_uid(user);
}

static void fanotify_free_event(struct fsnotify_event *fsn_event)
{
        struct fanotify_event *event;

        event = FANOTIFY_E(fsn_event);
        if (fanotify_event_has_path(event))
                path_put(&event->path);
        else if (fanotify_event_has_ext_fh(event))
                kfree(event->fid.ext_fh);
        put_pid(event->pid);
        if (fanotify_is_perm_event(event->mask)) {
                kmem_cache_free(fanotify_perm_event_cachep,
                                FANOTIFY_PE(fsn_event));
                return;
        }
        kmem_cache_free(fanotify_event_cachep, event);
}

static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
{
        kmem_cache_free(fanotify_mark_cache, fsn_mark);
}

const struct fsnotify_ops fanotify_fsnotify_ops = {
        .handle_event = fanotify_handle_event,
        .free_group_priv = fanotify_free_group_priv,
        .free_event = fanotify_free_event,
        .free_mark = fanotify_free_mark,
};