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254947d479
Implement code to derive a new set of creds for the cachefiles to use when making VFS or I/O calls and to change the auditing info since the application interacting with the network filesystem is not accessing the cache directly. Cachefiles uses override_creds() to change the effective creds temporarily. set_security_override_from_ctx() is called to derive the LSM 'label' that the cachefiles driver will act with. set_create_files_as() is called to determine the LSM 'label' that will be applied to files and directories created in the cache. These functions alter the new creds. Also implement a couple of functions to wrap the calls to begin/end cred overriding. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819627469.215744.3603633690679962985.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906928172.143852.15886637013364286786.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967138138.1823006.7620933448261939504.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021537001.640689.4081334436031700558.stgit@warthog.procyon.org.uk/ # v4
112 lines
2.5 KiB
C
112 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* CacheFiles security management
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*
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* Copyright (C) 2007, 2021 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/fs.h>
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#include <linux/cred.h>
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#include "internal.h"
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/*
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* determine the security context within which we access the cache from within
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* the kernel
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*/
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int cachefiles_get_security_ID(struct cachefiles_cache *cache)
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{
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struct cred *new;
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int ret;
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_enter("{%s}", cache->secctx);
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new = prepare_kernel_cred(current);
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if (!new) {
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ret = -ENOMEM;
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goto error;
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}
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if (cache->secctx) {
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ret = set_security_override_from_ctx(new, cache->secctx);
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if (ret < 0) {
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put_cred(new);
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pr_err("Security denies permission to nominate security context: error %d\n",
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ret);
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goto error;
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}
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}
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cache->cache_cred = new;
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ret = 0;
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error:
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_leave(" = %d", ret);
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return ret;
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}
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/*
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* see if mkdir and create can be performed in the root directory
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*/
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static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
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struct dentry *root)
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{
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int ret;
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ret = security_inode_mkdir(d_backing_inode(root), root, 0);
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if (ret < 0) {
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pr_err("Security denies permission to make dirs: error %d",
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ret);
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return ret;
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}
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ret = security_inode_create(d_backing_inode(root), root, 0);
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if (ret < 0)
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pr_err("Security denies permission to create files: error %d",
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ret);
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return ret;
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}
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/*
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* check the security details of the on-disk cache
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* - must be called with security override in force
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* - must return with a security override in force - even in the case of an
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* error
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*/
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int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
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struct dentry *root,
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const struct cred **_saved_cred)
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{
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struct cred *new;
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int ret;
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_enter("");
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/* duplicate the cache creds for COW (the override is currently in
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* force, so we can use prepare_creds() to do this) */
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new = prepare_creds();
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if (!new)
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return -ENOMEM;
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cachefiles_end_secure(cache, *_saved_cred);
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/* use the cache root dir's security context as the basis with
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* which create files */
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ret = set_create_files_as(new, d_backing_inode(root));
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if (ret < 0) {
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abort_creds(new);
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cachefiles_begin_secure(cache, _saved_cred);
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_leave(" = %d [cfa]", ret);
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return ret;
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}
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put_cred(cache->cache_cred);
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cache->cache_cred = new;
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cachefiles_begin_secure(cache, _saved_cred);
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ret = cachefiles_check_cache_dir(cache, root);
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if (ret == -EOPNOTSUPP)
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ret = 0;
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_leave(" = %d", ret);
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return ret;
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}
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