path: root/fs/overlayfs/util.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, Inc.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/file.h>
#include <linux/fileattr.h>
#include <linux/uuid.h>
#include <linux/namei.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

/* Get write access to upper mnt - may fail if upper sb was remounted ro */
int ovl_get_write_access(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	return mnt_get_write_access(ovl_upper_mnt(ofs));
}

/* Get write access to upper sb - may block if upper sb is frozen */
void ovl_start_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	sb_start_write(ovl_upper_mnt(ofs)->mnt_sb);
}

int ovl_want_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	return mnt_want_write(ovl_upper_mnt(ofs));
}

void ovl_put_write_access(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	mnt_put_write_access(ovl_upper_mnt(ofs));
}

void ovl_end_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	sb_end_write(ovl_upper_mnt(ofs)->mnt_sb);
}

void ovl_drop_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	mnt_drop_write(ovl_upper_mnt(ofs));
}

struct dentry *ovl_workdir(struct dentry *dentry)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
	return ofs->workdir;
}

const struct cred *ovl_override_creds(struct super_block *sb)
{
	struct ovl_fs *ofs = OVL_FS(sb);

	return override_creds(ofs->creator_cred);
}

/*
 * Check if underlying fs supports file handles and try to determine encoding
 * type, in order to deduce maximum inode number used by fs.
 *
 * Return 0 if file handles are not supported.
 * Return 1 (FILEID_INO32_GEN) if fs uses the default 32bit inode encoding.
 * Return -1 if fs uses a non default encoding with unknown inode size.
 */
int ovl_can_decode_fh(struct super_block *sb)
{
	if (!capable(CAP_DAC_READ_SEARCH))
		return 0;

	if (!exportfs_can_decode_fh(sb->s_export_op))
		return 0;

	return sb->s_export_op->encode_fh ? -1 : FILEID_INO32_GEN;
}

struct dentry *ovl_indexdir(struct super_block *sb)
{
	struct ovl_fs *ofs = OVL_FS(sb);

	return ofs->config.index ? ofs->workdir : NULL;
}

/* Index all files on copy up. For now only enabled for NFS export */
bool ovl_index_all(struct super_block *sb)
{
	struct ovl_fs *ofs = OVL_FS(sb);

	return ofs->config.nfs_export && ofs->config.index;
}

/* Verify lower origin on lookup. For now only enabled for NFS export */
bool ovl_verify_lower(struct super_block *sb)
{
	struct ovl_fs *ofs = OVL_FS(sb);

	return ofs->config.nfs_export && ofs->config.index;
}

struct ovl_path *ovl_stack_alloc(unsigned int n)
{
	return kcalloc(n, sizeof(struct ovl_path), GFP_KERNEL);
}

void ovl_stack_cpy(struct ovl_path *dst, struct ovl_path *src, unsigned int n)
{
	unsigned int i;

	memcpy(dst, src, sizeof(struct ovl_path) * n);
	for (i = 0; i < n; i++)
		dget(src[i].dentry);
}

void ovl_stack_put(struct ovl_path *stack, unsigned int n)
{
	unsigned int i;

	for (i = 0; stack && i < n; i++)
		dput(stack[i].dentry);
}

void ovl_stack_free(struct ovl_path *stack, unsigned int n)
{
	ovl_stack_put(stack, n);
	kfree(stack);
}

struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
	size_t size = offsetof(struct ovl_entry, __lowerstack[numlower]);
	struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);

	if (oe)
		oe->__numlower = numlower;

	return oe;
}

void ovl_free_entry(struct ovl_entry *oe)
{
	ovl_stack_put(ovl_lowerstack(oe), ovl_numlower(oe));
	kfree(oe);
}

#define OVL_D_REVALIDATE (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE)

bool ovl_dentry_remote(struct dentry *dentry)
{
	return dentry->d_flags & OVL_D_REVALIDATE;
}

void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *realdentry)
{
	if (!ovl_dentry_remote(realdentry))
		return;

	spin_lock(&dentry->d_lock);
	dentry->d_flags |= realdentry->d_flags & OVL_D_REVALIDATE;
	spin_unlock(&dentry->d_lock);
}

void ovl_dentry_init_reval(struct dentry *dentry, struct dentry *upperdentry,
			   struct ovl_entry *oe)
{
	return ovl_dentry_init_flags(dentry, upperdentry, oe, OVL_D_REVALIDATE);
}

void ovl_dentry_init_flags(struct dentry *dentry, struct dentry *upperdentry,
			   struct ovl_entry *oe, unsigned int mask)
{
	struct ovl_path *lowerstack = ovl_lowerstack(oe);
	unsigned int i, flags = 0;

	if (upperdentry)
		flags |= upperdentry->d_flags;
	for (i = 0; i < ovl_numlower(oe) && lowerstack[i].dentry; i++)
		flags |= lowerstack[i].dentry->d_flags;

	spin_lock(&dentry->d_lock);
	dentry->d_flags &= ~mask;
	dentry->d_flags |= flags & mask;
	spin_unlock(&dentry->d_lock);
}

bool ovl_dentry_weird(struct dentry *dentry)
{
	if (!d_can_lookup(dentry) && !d_is_file(dentry) && !d_is_symlink(dentry))
		return true;

	return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
				  DCACHE_MANAGE_TRANSIT |
				  DCACHE_OP_HASH |
				  DCACHE_OP_COMPARE);
}

enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
	struct ovl_entry *oe = OVL_E(dentry);
	enum ovl_path_type type = 0;

	if (ovl_dentry_upper(dentry)) {
		type = __OVL_PATH_UPPER;

		/*
		 * Non-dir dentry can hold lower dentry of its copy up origin.
		 */
		if (ovl_numlower(oe)) {
			if (ovl_test_flag(OVL_CONST_INO, d_inode(dentry)))
				type |= __OVL_PATH_ORIGIN;
			if (d_is_dir(dentry) ||
			    !ovl_has_upperdata(d_inode(dentry)))
				type |= __OVL_PATH_MERGE;
		}
	} else {
		if (ovl_numlower(oe) > 1)
			type |= __OVL_PATH_MERGE;
	}
	return type;
}

void ovl_path_upper(struct dentry *dentry, struct path *path)
{
	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);

	path->mnt = ovl_upper_mnt(ofs);
	path->dentry = ovl_dentry_upper(dentry);
}

void ovl_path_lower(struct dentry *dentry, struct path *path)
{
	struct ovl_entry *oe = OVL_E(dentry);
	struct ovl_path *lowerpath = ovl_lowerstack(oe);

	if (ovl_numlower(oe)) {
		path->mnt = lowerpath->layer->mnt;
		path->dentry = lowerpath->dentry;
	} else {
		*path = (struct path) { };
	}
}

void ovl_path_lowerdata(struct dentry *dentry, struct path *path)
{
	struct ovl_entry *oe = OVL_E(dentry);
	struct ovl_path *lowerdata = ovl_lowerdata(oe);
	struct dentry *lowerdata_dentry = ovl_lowerdata_dentry(oe);

	if (lowerdata_dentry) {
		path->dentry = lowerdata_dentry;
		/*
		 * Pairs with smp_wmb() in ovl_dentry_set_lowerdata().
		 * Make sure that if lowerdata->dentry is visible, then
		 * datapath->layer is visible as well.
		 */
		smp_rmb();
		path->mnt = READ_ONCE(lowerdata->layer)->mnt;
	} else {
		*path = (struct path) { };
	}
}

enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
{
	enum ovl_path_type type = ovl_path_type(dentry);

	if (!OVL_TYPE_UPPER(type))
		ovl_path_lower(dentry, path);
	else
		ovl_path_upper(dentry, path);

	return type;
}

enum ovl_path_type ovl_path_realdata(struct dentry *dentry, struct path *path)
{
	enum ovl_path_type type = ovl_path_type(dentry);

	WARN_ON_ONCE(d_is_dir(dentry));

	if (!OVL_TYPE_UPPER(type) || OVL_TYPE_MERGE(type))
		ovl_path_lowerdata(dentry, path);
	else
		ovl_path_upper(dentry, path);

	return type;
}

struct dentry *ovl_dentry_upper(struct dentry *dentry)
{
	struct inode *inode = d_inode(dentry);

	return inode ? ovl_upperdentry_dereference(OVL_I(inode)) : NULL;
}

struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
	struct ovl_e