![Miklos Szeredi](/assets/img/avatar_default.png)
Filesystems filter out extended attributes in the "trusted." domain for unprivlieged callers. Overlay calls underlying filesystem's method with elevated privs, so need to do the filtering in overlayfs too. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
480 lines
12 KiB
C
480 lines
12 KiB
C
/*
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*
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* Copyright (C) 2011 Novell 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/slab.h>
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#include <linux/cred.h>
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#include <linux/xattr.h>
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#include <linux/posix_acl.h>
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#include "overlayfs.h"
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int ovl_setattr(struct dentry *dentry, struct iattr *attr)
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{
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int err;
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struct dentry *upperdentry;
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const struct cred *old_cred;
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/*
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* Check for permissions before trying to copy-up. This is redundant
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* since it will be rechecked later by ->setattr() on upper dentry. But
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* without this, copy-up can be triggered by just about anybody.
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*
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* We don't initialize inode->size, which just means that
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* inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
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* check for a swapfile (which this won't be anyway).
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*/
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err = setattr_prepare(dentry, attr);
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if (err)
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return err;
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err = ovl_want_write(dentry);
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if (err)
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goto out;
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err = ovl_copy_up(dentry);
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if (!err) {
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upperdentry = ovl_dentry_upper(dentry);
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if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
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attr->ia_valid &= ~ATTR_MODE;
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inode_lock(upperdentry->d_inode);
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old_cred = ovl_override_creds(dentry->d_sb);
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err = notify_change(upperdentry, attr, NULL);
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revert_creds(old_cred);
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if (!err)
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ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
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inode_unlock(upperdentry->d_inode);
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}
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ovl_drop_write(dentry);
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out:
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return err;
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}
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int ovl_getattr(const struct path *path, struct kstat *stat,
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u32 request_mask, unsigned int flags)
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{
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struct dentry *dentry = path->dentry;
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enum ovl_path_type type;
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struct path realpath;
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const struct cred *old_cred;
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bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
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int err;
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type = ovl_path_real(dentry, &realpath);
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old_cred = ovl_override_creds(dentry->d_sb);
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err = vfs_getattr(&realpath, stat, request_mask, flags);
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if (err)
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goto out;
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/*
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* When all layers are on the same fs, all real inode number are
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* unique, so we use the overlay st_dev, which is friendly to du -x.
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*
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* We also use st_ino of the copy up origin, if we know it.
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* This guaranties constant st_dev/st_ino across copy up.
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*
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* If filesystem supports NFS export ops, this also guaranties
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* persistent st_ino across mount cycle.
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*/
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if (ovl_same_sb(dentry->d_sb)) {
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if (OVL_TYPE_ORIGIN(type)) {
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struct kstat lowerstat;
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u32 lowermask = STATX_INO | (!is_dir ? STATX_NLINK : 0);
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ovl_path_lower(dentry, &realpath);
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err = vfs_getattr(&realpath, &lowerstat,
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lowermask, flags);
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if (err)
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goto out;
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WARN_ON_ONCE(stat->dev != lowerstat.dev);
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/*
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* Lower hardlinks are broken on copy up to different
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* upper files, so we cannot use the lower origin st_ino
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* for those different files, even for the same fs case.
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*/
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if (is_dir || lowerstat.nlink == 1)
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stat->ino = lowerstat.ino;
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}
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stat->dev = dentry->d_sb->s_dev;
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} else if (is_dir) {
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/*
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* If not all layers are on the same fs the pair {real st_ino;
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* overlay st_dev} is not unique, so use the non persistent
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* overlay st_ino.
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*
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* Always use the overlay st_dev for directories, so 'find
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* -xdev' will scan the entire overlay mount and won't cross the
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* overlay mount boundaries.
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*/
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stat->dev = dentry->d_sb->s_dev;
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stat->ino = dentry->d_inode->i_ino;
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}
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/*
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* It's probably not worth it to count subdirs to get the
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* correct link count. nlink=1 seems to pacify 'find' and
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* other utilities.
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*/
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if (is_dir && OVL_TYPE_MERGE(type))
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stat->nlink = 1;
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out:
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revert_creds(old_cred);
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return err;
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}
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int ovl_permission(struct inode *inode, int mask)
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{
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bool is_upper;
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struct inode *realinode = ovl_inode_real(inode, &is_upper);
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const struct cred *old_cred;
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int err;
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/* Careful in RCU walk mode */
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if (!realinode) {
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WARN_ON(!(mask & MAY_NOT_BLOCK));
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return -ECHILD;
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}
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/*
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* Check overlay inode with the creds of task and underlying inode
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* with creds of mounter
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*/
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err = generic_permission(inode, mask);
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if (err)
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return err;
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old_cred = ovl_override_creds(inode->i_sb);
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if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
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mask &= ~(MAY_WRITE | MAY_APPEND);
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/* Make sure mounter can read file for copy up later */
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mask |= MAY_READ;
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}
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err = inode_permission(realinode, mask);
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revert_creds(old_cred);
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return err;
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}
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static const char *ovl_get_link(struct dentry *dentry,
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struct inode *inode,
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struct delayed_call *done)
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{
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const struct cred *old_cred;
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const char *p;
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if (!dentry)
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return ERR_PTR(-ECHILD);
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old_cred = ovl_override_creds(dentry->d_sb);
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p = vfs_get_link(ovl_dentry_real(dentry), done);
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revert_creds(old_cred);
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return p;
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}
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bool ovl_is_private_xattr(const char *name)
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{
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return strncmp(name, OVL_XATTR_PREFIX,
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sizeof(OVL_XATTR_PREFIX) - 1) == 0;
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}
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int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
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size_t size, int flags)
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{
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int err;
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struct path realpath;
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enum ovl_path_type type = ovl_path_real(dentry, &realpath);
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const struct cred *old_cred;
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err = ovl_want_write(dentry);
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if (err)
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goto out;
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if (!value && !OVL_TYPE_UPPER(type)) {
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err = vfs_getxattr(realpath.dentry, name, NULL, 0);
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if (err < 0)
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goto out_drop_write;
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}
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err = ovl_copy_up(dentry);
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if (err)
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goto out_drop_write;
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if (!OVL_TYPE_UPPER(type))
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ovl_path_upper(dentry, &realpath);
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old_cred = ovl_override_creds(dentry->d_sb);
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if (value)
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err = vfs_setxattr(realpath.dentry, name, value, size, flags);
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else {
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WARN_ON(flags != XATTR_REPLACE);
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err = vfs_removexattr(realpath.dentry, name);
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}
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revert_creds(old_cred);
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out_drop_write:
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ovl_drop_write(dentry);
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out:
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return err;
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}
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int ovl_xattr_get(struct dentry *dentry, const char *name,
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void *value, size_t size)
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{
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struct dentry *realdentry = ovl_dentry_real(dentry);
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ssize_t res;
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const struct cred *old_cred;
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old_cred = ovl_override_creds(dentry->d_sb);
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res = vfs_getxattr(realdentry, name, value, size);
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revert_creds(old_cred);
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return res;
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}
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static bool ovl_can_list(const char *s)
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{
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/* List all non-trusted xatts */
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if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
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return true;
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/* Never list trusted.overlay, list other trusted for superuser only */
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return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
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}
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ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
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{
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struct dentry *realdentry = ovl_dentry_real(dentry);
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ssize_t res;
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size_t len;
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char *s;
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const struct cred *old_cred;
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old_cred = ovl_override_creds(dentry->d_sb);
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res = vfs_listxattr(realdentry, list, size);
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revert_creds(old_cred);
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if (res <= 0 || size == 0)
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return res;
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/* filter out private xattrs */
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for (s = list, len = res; len;) {
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size_t slen = strnlen(s, len) + 1;
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/* underlying fs providing us with an broken xattr list? */
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if (WARN_ON(slen > len))
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return -EIO;
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len -= slen;
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if (!ovl_can_list(s)) {
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res -= slen;
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memmove(s, s + slen, len);
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} else {
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s += slen;
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}
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}
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return res;
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}
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struct posix_acl *ovl_get_acl(struct inode *inode, int type)
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{
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struct inode *realinode = ovl_inode_real(inode, NULL);
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const struct cred *old_cred;
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struct posix_acl *acl;
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if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
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return NULL;
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old_cred = ovl_override_creds(inode->i_sb);
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acl = get_acl(realinode, type);
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revert_creds(old_cred);
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return acl;
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}
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static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
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struct dentry *realdentry)
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{
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if (OVL_TYPE_UPPER(type))
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return false;
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if (special_file(realdentry->d_inode->i_mode))
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return false;
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if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
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return false;
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return true;
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}
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int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
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{
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int err = 0;
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struct path realpath;
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enum ovl_path_type type;
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type = ovl_path_real(dentry, &realpath);
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if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
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err = ovl_want_write(dentry);
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if (!err) {
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err = ovl_copy_up_flags(dentry, file_flags);
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ovl_drop_write(dentry);
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}
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}
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return err;
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}
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int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
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{
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struct dentry *alias;
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struct path upperpath;
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if (!(flags & S_ATIME))
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return 0;
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alias = d_find_any_alias(inode);
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if (!alias)
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return 0;
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ovl_path_upper(alias, &upperpath);
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if (upperpath.dentry) {
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touch_atime(&upperpath);
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inode->i_atime = d_inode(upperpath.dentry)->i_atime;
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}
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dput(alias);
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return 0;
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}
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static const struct inode_operations ovl_file_inode_operations = {
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.setattr = ovl_setattr,
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.permission = ovl_permission,
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.getattr = ovl_getattr,
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.listxattr = ovl_listxattr,
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.get_acl = ovl_get_acl,
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.update_time = ovl_update_time,
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};
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static const struct inode_operations ovl_symlink_inode_operations = {
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.setattr = ovl_setattr,
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.get_link = ovl_get_link,
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.getattr = ovl_getattr,
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.listxattr = ovl_listxattr,
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.update_time = ovl_update_time,
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};
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/*
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* It is possible to stack overlayfs instance on top of another
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* overlayfs instance as lower layer. We need to annonate the
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* stackable i_mutex locks according to stack level of the super
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* block instance. An overlayfs instance can never be in stack
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* depth 0 (there is always a real fs below it). An overlayfs
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* inode lock will use the lockdep annotaion ovl_i_mutex_key[depth].
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*
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* For example, here is a snip from /proc/lockdep_chains after
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* dir_iterate of nested overlayfs:
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*
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* [...] &ovl_i_mutex_dir_key[depth] (stack_depth=2)
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* [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1)
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* [...] &type->i_mutex_dir_key (stack_depth=0)
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*/
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#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH
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static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
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{
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#ifdef CONFIG_LOCKDEP
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static struct lock_class_key ovl_i_mutex_key[OVL_MAX_NESTING];
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static struct lock_class_key ovl_i_mutex_dir_key[OVL_MAX_NESTING];
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int depth = inode->i_sb->s_stack_depth - 1;
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if (WARN_ON_ONCE(depth < 0 || depth >= OVL_MAX_NESTING))
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depth = 0;
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if (S_ISDIR(inode->i_mode))
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lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_dir_key[depth]);
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else
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lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_key[depth]);
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#endif
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}
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static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
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{
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inode->i_ino = get_next_ino();
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inode->i_mode = mode;
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inode->i_flags |= S_NOCMTIME;
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#ifdef CONFIG_FS_POSIX_ACL
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inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
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#endif
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ovl_lockdep_annotate_inode_mutex_key(inode);
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switch (mode & S_IFMT) {
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case S_IFREG:
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inode->i_op = &ovl_file_inode_operations;
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break;
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case S_IFDIR:
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inode->i_op = &ovl_dir_inode_operations;
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inode->i_fop = &ovl_dir_operations;
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break;
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case S_IFLNK:
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inode->i_op = &ovl_symlink_inode_operations;
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break;
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default:
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inode->i_op = &ovl_file_inode_operations;
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init_special_inode(inode, mode, rdev);
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break;
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}
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}
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struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
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{
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struct inode *inode;
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inode = new_inode(sb);
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if (inode)
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ovl_fill_inode(inode, mode, rdev);
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return inode;
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}
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static int ovl_inode_test(struct inode *inode, void *data)
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{
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return ovl_inode_real(inode, NULL) == data;
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}
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static int ovl_inode_set(struct inode *inode, void *data)
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{
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inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
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return 0;
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}
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struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
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{
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struct inode *inode;
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inode = iget5_locked(sb, (unsigned long) realinode,
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ovl_inode_test, ovl_inode_set, realinode);
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if (inode && inode->i_state & I_NEW) {
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ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
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set_nlink(inode, realinode->i_nlink);
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unlock_new_inode(inode);
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}
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return inode;
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}
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