![Miklos Szeredi](/assets/img/avatar_default.png)
If a directory has the "trusted.overlay.redirect" xattr, it means that the value of the xattr should be used to find the underlying directory on the next lower layer. The redirect may be relative or absolute. Absolute redirects begin with a slash. A relative redirect means: instead of the current dentry's name use the value of the redirect to find the directory in the next lower layer. Relative redirects must not contain a slash. An absolute redirect means: look up the directory relative to the root of the overlay using the value of the redirect in the next lower layer. Redirects work on lower layers as well. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
402 lines
8.4 KiB
C
402 lines
8.4 KiB
C
/*
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* Copyright (C) 2011 Novell Inc.
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* Copyright (C) 2016 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*/
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#include <linux/fs.h>
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#include <linux/namei.h>
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#include <linux/xattr.h>
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#include <linux/ratelimit.h>
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#include "overlayfs.h"
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#include "ovl_entry.h"
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struct ovl_lookup_data {
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struct qstr name;
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bool is_dir;
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bool opaque;
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bool stop;
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bool last;
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char *redirect;
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};
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static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
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size_t prelen, const char *post)
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{
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int res;
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char *s, *next, *buf = NULL;
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res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
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if (res < 0) {
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if (res == -ENODATA || res == -EOPNOTSUPP)
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return 0;
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goto fail;
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}
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buf = kzalloc(prelen + res + strlen(post) + 1, GFP_TEMPORARY);
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if (!buf)
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return -ENOMEM;
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if (res == 0)
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goto invalid;
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res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
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if (res < 0)
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goto fail;
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if (res == 0)
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goto invalid;
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if (buf[0] == '/') {
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for (s = buf; *s++ == '/'; s = next) {
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next = strchrnul(s, '/');
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if (s == next)
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goto invalid;
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}
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} else {
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if (strchr(buf, '/') != NULL)
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goto invalid;
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memmove(buf + prelen, buf, res);
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memcpy(buf, d->name.name, prelen);
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}
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strcat(buf, post);
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kfree(d->redirect);
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d->redirect = buf;
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d->name.name = d->redirect;
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d->name.len = strlen(d->redirect);
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return 0;
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err_free:
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kfree(buf);
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return 0;
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fail:
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pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
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goto err_free;
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invalid:
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pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
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goto err_free;
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}
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static bool ovl_is_opaquedir(struct dentry *dentry)
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{
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int res;
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char val;
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if (!d_is_dir(dentry))
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return false;
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res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
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if (res == 1 && val == 'y')
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return true;
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return false;
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}
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static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
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const char *name, unsigned int namelen,
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size_t prelen, const char *post,
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struct dentry **ret)
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{
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struct dentry *this;
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int err;
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this = lookup_one_len_unlocked(name, base, namelen);
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if (IS_ERR(this)) {
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err = PTR_ERR(this);
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this = NULL;
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if (err == -ENOENT || err == -ENAMETOOLONG)
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goto out;
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goto out_err;
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}
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if (!this->d_inode)
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goto put_and_out;
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if (ovl_dentry_weird(this)) {
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/* Don't support traversing automounts and other weirdness */
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err = -EREMOTE;
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goto out_err;
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}
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if (ovl_is_whiteout(this)) {
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d->stop = d->opaque = true;
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goto put_and_out;
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}
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if (!d_can_lookup(this)) {
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d->stop = true;
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if (d->is_dir)
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goto put_and_out;
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goto out;
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}
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d->is_dir = true;
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if (!d->last && ovl_is_opaquedir(this)) {
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d->stop = d->opaque = true;
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goto out;
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}
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err = ovl_check_redirect(this, d, prelen, post);
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if (err)
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goto out_err;
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out:
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*ret = this;
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return 0;
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put_and_out:
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dput(this);
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this = NULL;
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goto out;
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out_err:
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dput(this);
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return err;
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}
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static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
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struct dentry **ret)
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{
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const char *s = d->name.name;
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struct dentry *dentry = NULL;
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int err;
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if (*s != '/')
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return ovl_lookup_single(base, d, d->name.name, d->name.len,
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0, "", ret);
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while (*s++ == '/' && !IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
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const char *next = strchrnul(s, '/');
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size_t slen = strlen(s);
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if (WARN_ON(slen > d->name.len) ||
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WARN_ON(strcmp(d->name.name + d->name.len - slen, s)))
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return -EIO;
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err = ovl_lookup_single(base, d, s, next - s,
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d->name.len - slen, next, &base);
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dput(dentry);
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if (err)
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return err;
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dentry = base;
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s = next;
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}
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*ret = dentry;
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return 0;
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}
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/*
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* Returns next layer in stack starting from top.
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* Returns -1 if this is the last layer.
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*/
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int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
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{
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struct ovl_entry *oe = dentry->d_fsdata;
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BUG_ON(idx < 0);
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if (idx == 0) {
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ovl_path_upper(dentry, path);
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if (path->dentry)
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return oe->numlower ? 1 : -1;
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idx++;
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}
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BUG_ON(idx > oe->numlower);
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*path = oe->lowerstack[idx - 1];
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return (idx < oe->numlower) ? idx + 1 : -1;
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}
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struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
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unsigned int flags)
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{
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struct ovl_entry *oe;
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const struct cred *old_cred;
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struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
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struct ovl_entry *poe = dentry->d_parent->d_fsdata;
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struct path *stack = NULL;
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struct dentry *upperdir, *upperdentry = NULL;
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unsigned int ctr = 0;
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struct inode *inode = NULL;
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bool upperopaque = false;
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char *upperredirect = NULL;
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struct dentry *this;
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unsigned int i;
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int err;
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struct ovl_lookup_data d = {
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.name = dentry->d_name,
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.is_dir = false,
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.opaque = false,
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.stop = false,
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.last = !poe->numlower,
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.redirect = NULL,
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};
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if (dentry->d_name.len > ofs->namelen)
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return ERR_PTR(-ENAMETOOLONG);
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old_cred = ovl_override_creds(dentry->d_sb);
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upperdir = ovl_upperdentry_dereference(poe);
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if (upperdir) {
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err = ovl_lookup_layer(upperdir, &d, &upperdentry);
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if (err)
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goto out;
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if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
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dput(upperdentry);
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err = -EREMOTE;
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goto out;
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}
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if (d.redirect) {
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upperredirect = kstrdup(d.redirect, GFP_KERNEL);
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if (!upperredirect)
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goto out_put_upper;
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if (d.redirect[0] == '/')
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poe = dentry->d_sb->s_root->d_fsdata;
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}
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upperopaque = d.opaque;
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}
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if (!d.stop && poe->numlower) {
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err = -ENOMEM;
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stack = kcalloc(ofs->numlower, sizeof(struct path),
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GFP_TEMPORARY);
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if (!stack)
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goto out_put_upper;
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}
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for (i = 0; !d.stop && i < poe->numlower; i++) {
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struct path lowerpath = poe->lowerstack[i];
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d.last = i == poe->numlower - 1;
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err = ovl_lookup_layer(lowerpath.dentry, &d, &this);
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if (err)
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goto out_put;
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if (!this)
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continue;
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stack[ctr].dentry = this;
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stack[ctr].mnt = lowerpath.mnt;
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ctr++;
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if (d.stop)
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break;
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if (d.redirect &&
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d.redirect[0] == '/' &&
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poe != dentry->d_sb->s_root->d_fsdata) {
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poe = dentry->d_sb->s_root->d_fsdata;
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/* Find the current layer on the root dentry */
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for (i = 0; i < poe->numlower; i++)
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if (poe->lowerstack[i].mnt == lowerpath.mnt)
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break;
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if (WARN_ON(i == poe->numlower))
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break;
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}
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}
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oe = ovl_alloc_entry(ctr);
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err = -ENOMEM;
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if (!oe)
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goto out_put;
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if (upperdentry || ctr) {
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struct dentry *realdentry;
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struct inode *realinode;
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realdentry = upperdentry ? upperdentry : stack[0].dentry;
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realinode = d_inode(realdentry);
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err = -ENOMEM;
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if (upperdentry && !d_is_dir(upperdentry)) {
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inode = ovl_get_inode(dentry->d_sb, realinode);
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} else {
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inode = ovl_new_inode(dentry->d_sb, realinode->i_mode,
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realinode->i_rdev);
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if (inode)
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ovl_inode_init(inode, realinode, !!upperdentry);
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}
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if (!inode)
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goto out_free_oe;
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ovl_copyattr(realdentry->d_inode, inode);
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}
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revert_creds(old_cred);
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oe->opaque = upperopaque;
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oe->redirect = upperredirect;
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oe->__upperdentry = upperdentry;
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memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
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kfree(stack);
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kfree(d.redirect);
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dentry->d_fsdata = oe;
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d_add(dentry, inode);
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return NULL;
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out_free_oe:
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kfree(oe);
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out_put:
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for (i = 0; i < ctr; i++)
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dput(stack[i].dentry);
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kfree(stack);
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out_put_upper:
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dput(upperdentry);
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kfree(upperredirect);
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out:
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kfree(d.redirect);
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revert_creds(old_cred);
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return ERR_PTR(err);
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}
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bool ovl_lower_positive(struct dentry *dentry)
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{
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struct ovl_entry *oe = dentry->d_fsdata;
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struct ovl_entry *poe = dentry->d_parent->d_fsdata;
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const struct qstr *name = &dentry->d_name;
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unsigned int i;
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bool positive = false;
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bool done = false;
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/*
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* If dentry is negative, then lower is positive iff this is a
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* whiteout.
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*/
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if (!dentry->d_inode)
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return oe->opaque;
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/* Negative upper -> positive lower */
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if (!oe->__upperdentry)
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return true;
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/* Positive upper -> have to look up lower to see whether it exists */
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for (i = 0; !done && !positive && i < poe->numlower; i++) {
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struct dentry *this;
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struct dentry *lowerdir = poe->lowerstack[i].dentry;
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this = lookup_one_len_unlocked(name->name, lowerdir,
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name->len);
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if (IS_ERR(this)) {
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switch (PTR_ERR(this)) {
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case -ENOENT:
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case -ENAMETOOLONG:
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break;
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default:
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/*
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* Assume something is there, we just couldn't
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* access it.
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*/
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positive = true;
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break;
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}
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} else {
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if (this->d_inode) {
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positive = !ovl_is_whiteout(this);
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done = true;
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}
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dput(this);
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}
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}
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return positive;
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}
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