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kernel/linux-imx6_3.14.28/fs/cachefiles/security.c 2.77 KB
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  /* CacheFiles security management
   *
   * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public Licence
   * as published by the Free Software Foundation; either version
   * 2 of the Licence, or (at your option) any later version.
   */
  
  #include <linux/fs.h>
  #include <linux/cred.h>
  #include "internal.h"
  
  /*
   * determine the security context within which we access the cache from within
   * the kernel
   */
  int cachefiles_get_security_ID(struct cachefiles_cache *cache)
  {
  	struct cred *new;
  	int ret;
  
  	_enter("{%s}", cache->secctx);
  
  	new = prepare_kernel_cred(current);
  	if (!new) {
  		ret = -ENOMEM;
  		goto error;
  	}
  
  	if (cache->secctx) {
  		ret = set_security_override_from_ctx(new, cache->secctx);
  		if (ret < 0) {
  			put_cred(new);
  			printk(KERN_ERR "CacheFiles:"
  			       " Security denies permission to nominate"
  			       " security context: error %d
  ",
  			       ret);
  			goto error;
  		}
  	}
  
  	cache->cache_cred = new;
  	ret = 0;
  error:
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * see if mkdir and create can be performed in the root directory
   */
  static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
  				      struct dentry *root)
  {
  	int ret;
  
  	ret = security_inode_mkdir(root->d_inode, root, 0);
  	if (ret < 0) {
  		printk(KERN_ERR "CacheFiles:"
  		       " Security denies permission to make dirs: error %d",
  		       ret);
  		return ret;
  	}
  
  	ret = security_inode_create(root->d_inode, root, 0);
  	if (ret < 0)
  		printk(KERN_ERR "CacheFiles:"
  		       " Security denies permission to create files: error %d",
  		       ret);
  
  	return ret;
  }
  
  /*
   * check the security details of the on-disk cache
   * - must be called with security override in force
   * - must return with a security override in force - even in the case of an
   *   error
   */
  int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
  					struct dentry *root,
  					const struct cred **_saved_cred)
  {
  	struct cred *new;
  	int ret;
  
  	_enter("");
  
  	/* duplicate the cache creds for COW (the override is currently in
  	 * force, so we can use prepare_creds() to do this) */
  	new = prepare_creds();
  	if (!new)
  		return -ENOMEM;
  
  	cachefiles_end_secure(cache, *_saved_cred);
  
  	/* use the cache root dir's security context as the basis with
  	 * which create files */
  	ret = set_create_files_as(new, root->d_inode);
  	if (ret < 0) {
  		abort_creds(new);
  		cachefiles_begin_secure(cache, _saved_cred);
  		_leave(" = %d [cfa]", ret);
  		return ret;
  	}
  
  	put_cred(cache->cache_cred);
  	cache->cache_cred = new;
  
  	cachefiles_begin_secure(cache, _saved_cred);
  	ret = cachefiles_check_cache_dir(cache, root);
  
  	if (ret == -EOPNOTSUPP)
  		ret = 0;
  	_leave(" = %d", ret);
  	return ret;
  }