// SPDX-License-Identifier: GPL-2.0-only
/*
 * fs/kernfs/inode.c - kernfs inode implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
 */

#include <linux/pagemap.h>
#include <linux/backing-dev.h>
#include <linux/capability.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/xattr.h>
#include <linux/security.h>

#include "kernfs-internal.h"

static const struct inode_operations kernfs_iops = {
        .permission     = kernfs_iop_permission,
        .setattr        = kernfs_iop_setattr,
        .getattr        = kernfs_iop_getattr,
        .listxattr      = kernfs_iop_listxattr,
};

static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, bool alloc)
{
        struct kernfs_iattrs *ret __free(kfree) = NULL;
        struct kernfs_iattrs *attr;

        attr = READ_ONCE(kn->iattr);
        if (attr || !alloc)
                return attr;

        ret = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
        if (!ret)
                return NULL;

        /* assign default attributes */
        ret->ia_uid = GLOBAL_ROOT_UID;
        ret->ia_gid = GLOBAL_ROOT_GID;

        ktime_get_real_ts64(&ret->ia_atime);
        ret->ia_mtime = ret->ia_atime;
        ret->ia_ctime = ret->ia_atime;

        simple_xattrs_init(&ret->xattrs);
        atomic_set(&ret->nr_user_xattrs, 0);
        atomic_set(&ret->user_xattr_size, 0);

        /* If someone raced us, recognize it. */
        if (!try_cmpxchg(&kn->iattr, &attr, ret))
                return READ_ONCE(kn->iattr);

        return no_free_ptr(ret);
}

static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
{
        return __kernfs_iattrs(kn, true);
}

static struct kernfs_iattrs *kernfs_iattrs_noalloc(struct kernfs_node *kn)
{
        return __kernfs_iattrs(kn, false);
}

int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
{
        struct kernfs_iattrs *attrs;
        unsigned int ia_valid = iattr->ia_valid;

        attrs = kernfs_iattrs(kn);
        if (!attrs)
                return -ENOMEM;

        if (ia_valid & ATTR_UID)
                attrs->ia_uid = iattr->ia_uid;
        if (ia_valid & ATTR_GID)
                attrs->ia_gid = iattr->ia_gid;
        if (ia_valid & ATTR_ATIME)
                attrs->ia_atime = iattr->ia_atime;
        if (ia_valid & ATTR_MTIME)
                attrs->ia_mtime = iattr->ia_mtime;
        if (ia_valid & ATTR_CTIME)
                attrs->ia_ctime = iattr->ia_ctime;
        if (ia_valid & ATTR_MODE)
                kn->mode = iattr->ia_mode;
        return 0;
}

/**
 * kernfs_setattr - set iattr on a node
 * @kn: target node
 * @iattr: iattr to set
 *
 * Return: %0 on success, -errno on failure.
 */
int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
{
        int ret;
        struct kernfs_root *root = kernfs_root(kn);

        down_write(&root->kernfs_iattr_rwsem);
        ret = __kernfs_setattr(kn, iattr);
        up_write(&root->kernfs_iattr_rwsem);
        return ret;
}

int kernfs_iop_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
                       struct iattr *iattr)
{
        struct inode *inode = d_inode(dentry);
        struct kernfs_node *kn = inode->i_private;
        struct kernfs_root *root;
        int error;

        if (!kn)
                return -EINVAL;

        root = kernfs_root(kn);
        down_write(&root->kernfs_iattr_rwsem);
        error = setattr_prepare(&nop_mnt_idmap, dentry, iattr);
        if (error)
                goto out;

        error = __kernfs_setattr(kn, iattr);
        if (error)
                goto out;

        /* this ignores size changes */
        setattr_copy(&nop_mnt_idmap, inode, iattr);

out:
        up_write(&root->kernfs_iattr_rwsem);
        return error;
}

ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size)
{
        struct kernfs_node *kn = kernfs_dentry_node(dentry);
        struct kernfs_iattrs *attrs;

        attrs = kernfs_iattrs(kn);
        if (!attrs)
                return -ENOMEM;

        return simple_xattr_list(d_inode(dentry), &attrs->xattrs, buf, size);
}

static inline void set_default_inode_attr(struct inode *inode, umode_t mode)
{
        inode->i_mode = mode;
        simple_inode_init_ts(inode);
}

static inline void set_inode_attr(struct inode *inode,
                                  struct kernfs_iattrs *attrs)
{
        inode->i_uid = attrs->ia_uid;
        inode->i_gid = attrs->ia_gid;
        inode_set_atime_to_ts(inode, attrs->ia_atime);
        inode_set_mtime_to_ts(inode, attrs->ia_mtime);
        inode_set_ctime_to_ts(inode, attrs->ia_ctime);
}

static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)
{
        struct kernfs_iattrs *attrs;

        inode->i_mode = kn->mode;
        attrs = kernfs_iattrs_noalloc(kn);
        if (attrs)
                /*
                 * kernfs_node has non-default attributes get them from
                 * persistent copy in kernfs_node.
                 */
                set_inode_attr(inode, attrs);

        if (kernfs_type(kn) == KERNFS_DIR)
                set_nlink(inode, kn->dir.subdirs + 2);
}

int kernfs_iop_getattr(struct mnt_idmap *idmap,
                       const struct path *path, struct kstat *stat,
                       u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = d_inode(path->dentry);
        struct kernfs_node *kn = inode->i_private;
        struct kernfs_root *root = kernfs_root(kn);

        down_read(&root->kernfs_iattr_rwsem);
        kernfs_refresh_inode(kn, inode);
        generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
        up_read(&root->kernfs_iattr_rwsem);

        return 0;
}

static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
{
        kernfs_get(kn);
        inode->i_private = kn;
        inode->i_mapping->a_ops = &ram_aops;
        inode->i_op = &kernfs_iops;
        inode->i_generation = kernfs_gen(kn);

        set_default_inode_attr(inode, kn->mode);
        kernfs_refresh_inode(kn, inode);

        /* initialize inode according to type */
        switch (kernfs_type(kn)) {
        case KERNFS_DIR:
                inode->i_op = &kernfs_dir_iops;
                inode->i_fop = &kernfs_dir_fops;
                if (kn->flags & KERNFS_EMPTY_DIR)
                        make_empty_dir_inode(inode);
                break;
        case KERNFS_FILE:
                inode->i_size = kn->attr.size;
                inode->i_fop = &kernfs_file_fops;
                break;
        case KERNFS_LINK:
                inode->i_op = &kernfs_symlink_iops;
                break;
        default:
                BUG();
        }

        unlock_new_inode(inode);
}

/**
 *      kernfs_get_inode - get inode for kernfs_node
 *      @sb: super block
 *      @kn: kernfs_node to allocate inode for
 *
 *      Get inode for @kn.  If such inode doesn't exist, a new inode is
 *      allocated and basics are initialized.  New inode is returned
 *      locked.
 *
 *      Locking:
 *      Kernel thread context (may sleep).
 *
 *      Return:
 *      Pointer to allocated inode on success, %NULL on failure.
 */
struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
{
        struct inode *inode;

        inode = iget_locked(sb, kernfs_ino(kn));
        if (inode && (inode_state_read_once(inode) & I_NEW))
                kernfs_init_inode(kn, inode);

        return inode;
}

/*
 * The kernfs_node serves as both an inode and a directory entry for
 * kernfs.  To prevent the kernfs inode numbers from being freed
 * prematurely we take a reference to kernfs_node from the kernfs inode.  A
 * super_operations.evict_inode() implementation is needed to drop that
 * reference upon inode destruction.
 */
void kernfs_evict_inode(struct inode *inode)
{
        struct kernfs_node *kn = inode->i_private;

        truncate_inode_pages_final(&inode->i_data);
        clear_inode(inode);
        kernfs_put(kn);
}

int kernfs_iop_permission(struct mnt_idmap *idmap,
                          struct inode *inode, int mask)
{
        struct kernfs_node *kn;
        struct kernfs_root *root;
        int ret;

        if (mask & MAY_NOT_BLOCK)
                return -ECHILD;

        kn = inode->i_private;
        root = kernfs_root(kn);

        down_read(&root->kernfs_iattr_rwsem);
        kernfs_refresh_inode(kn, inode);
        ret = generic_permission(&nop_mnt_idmap, inode, mask);
        up_read(&root->kernfs_iattr_rwsem);

        return ret;
}

int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
                     void *value, size_t size)
{
        struct kernfs_iattrs *attrs = kernfs_iattrs_noalloc(kn);
        if (!attrs)
                return -ENODATA;

        return simple_xattr_get(&attrs->xattrs, name, value, size);
}

int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
                     const void *value, size_t size, int flags)
{
        struct simple_xattr *old_xattr;
        struct kernfs_iattrs *attrs;

        attrs = kernfs_iattrs(kn);
        if (!attrs)
                return -ENOMEM;

        old_xattr = simple_xattr_set(&attrs->xattrs, name, value, size, flags);
        if (IS_ERR(old_xattr))
                return PTR_ERR(old_xattr);

        simple_xattr_free(old_xattr);
        return 0;
}

static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,
                                struct dentry *unused, struct inode *inode,
                                const char *suffix, void *value, size_t size)
{
        const char *name = xattr_full_name(handler, suffix);
        struct kernfs_node *kn = inode->i_private;

        return kernfs_xattr_get(kn, name, value, size);
}

static int kernfs_vfs_xattr_set(const struct xattr_handler *handler,
                                struct mnt_idmap *idmap,
                                struct dentry *unused, struct inode *inode,
                                const char *suffix, const void *value,
                                size_t size, int flags)
{
        const char *name = xattr_full_name(handler, suffix);
        struct kernfs_node *kn = inode->i_private;

        return kernfs_xattr_set(kn, name, value, size, flags);
}

static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
                                     const char *full_name,
                                     struct simple_xattrs *xattrs,
                                     const void *value, size_t size, int flags)
{
        struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);
        atomic_t *sz = &attr->user_xattr_size;
        atomic_t *nr = &attr->nr_user_xattrs;
        struct simple_xattr *old_xattr;
        int ret;

        if (atomic_inc_return(nr) > KERNFS_MAX_USER_XATTRS) {
                ret = -ENOSPC;
                goto dec_count_out;
        }

        if (atomic_add_return(size, sz) > KERNFS_USER_XATTR_SIZE_LIMIT) {
                ret = -ENOSPC;
                goto dec_size_out;
        }

        old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);
        if (!old_xattr)
                return 0;

        if (IS_ERR(old_xattr)) {
                ret = PTR_ERR(old_xattr);
                goto dec_size_out;
        }

        ret = 0;
        size = old_xattr->size;
        simple_xattr_free(old_xattr);
dec_size_out:
        atomic_sub(size, sz);
dec_count_out:
        atomic_dec(nr);
        return ret;
}

static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn,
                                    const char *full_name,
                                    struct simple_xattrs *xattrs,
                                    const void *value, size_t size, int flags)
{
        struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);
        atomic_t *sz = &attr->user_xattr_size;
        atomic_t *nr = &attr->nr_user_xattrs;
        struct simple_xattr *old_xattr;

        old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);
        if (!old_xattr)
                return 0;

        if (IS_ERR(old_xattr))
                return PTR_ERR(old_xattr);

        atomic_sub(old_xattr->size, sz);
        atomic_dec(nr);
        simple_xattr_free(old_xattr);
        return 0;
}

static int kernfs_vfs_user_xattr_set(const struct xattr_handler *handler,
                                     struct mnt_idmap *idmap,
                                     struct dentry *unused, struct inode *inode,
                                     const char *suffix, const void *value,
                                     size_t size, int flags)
{
        const char *full_name = xattr_full_name(handler, suffix);
        struct kernfs_node *kn = inode->i_private;
        struct kernfs_iattrs *attrs;

        if (!(kernfs_root(kn)->flags & KERNFS_ROOT_SUPPORT_USER_XATTR))
                return -EOPNOTSUPP;

        attrs = kernfs_iattrs(kn);
        if (!attrs)
                return -ENOMEM;

        if (value)
                return kernfs_vfs_user_xattr_add(kn, full_name, &attrs->xattrs,
                                                 value, size, flags);
        else
                return kernfs_vfs_user_xattr_rm(kn, full_name, &attrs->xattrs,
                                                value, size, flags);

}

static const struct xattr_handler kernfs_trusted_xattr_handler = {
        .prefix = XATTR_TRUSTED_PREFIX,
        .get = kernfs_vfs_xattr_get,
        .set = kernfs_vfs_xattr_set,
};

static const struct xattr_handler kernfs_security_xattr_handler = {
        .prefix = XATTR_SECURITY_PREFIX,
        .get = kernfs_vfs_xattr_get,
        .set = kernfs_vfs_xattr_set,
};

static const struct xattr_handler kernfs_user_xattr_handler = {
        .prefix = XATTR_USER_PREFIX,
        .get = kernfs_vfs_xattr_get,
        .set = kernfs_vfs_user_xattr_set,
};

const struct xattr_handler * const kernfs_xattr_handlers[] = {
        &kernfs_trusted_xattr_handler,
        &kernfs_security_xattr_handler,
        &kernfs_user_xattr_handler,
        NULL
};