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e5a8b6446c
Instead of storing an opaque string, call security_secctx_to_secid() right in the "secctx" command handler and store only the numeric "secid". This eliminates an unnecessary string allocation and allows the daemon to receive errors when writing the "secctx" command instead of postponing the error to the "bind" command handler. For example, if the kernel was built without `CONFIG_SECURITY`, "bind" will return `EOPNOTSUPP`, but the daemon doesn't know why. With this patch, the "secctx" will instead return `EOPNOTSUPP` which is the right context for this error. This patch adds a boolean flag `have_secid` because I'm not sure if we can safely assume that zero is the special secid value for "not set". This appears to be true for SELinux, Smack and AppArmor, but since this attribute is not documented, I'm unable to derive a stable guarantee for that. Signed-off-by: Max Kellermann <max.kellermann@ionos.com> Signed-off-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20241209141554.638708-1-max.kellermann@ionos.com/ Link: https://lore.kernel.org/r/20241213135013.2964079-6-dhowells@redhat.com Signed-off-by: Christian Brauner <brauner@kernel.org>
113 lines
2.5 KiB
C
113 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("{%u}", cache->have_secid ? cache->secid : 0);
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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->have_secid) {
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ret = set_security_override(new, cache->secid);
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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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