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-rw-r--r--fs/cachefiles/security.c112
1 files changed, 112 insertions, 0 deletions
diff --git a/fs/cachefiles/security.c b/fs/cachefiles/security.c
new file mode 100644
index 000000000..fe777164f
--- /dev/null
+++ b/fs/cachefiles/security.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* CacheFiles security management
+ *
+ * Copyright (C) 2007, 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#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);
+ pr_err("Security denies permission to nominate security context: error %d\n",
+ 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(d_backing_inode(root), root, 0);
+ if (ret < 0) {
+ pr_err("Security denies permission to make dirs: error %d",
+ ret);
+ return ret;
+ }
+
+ ret = security_inode_create(d_backing_inode(root), root, 0);
+ if (ret < 0)
+ pr_err("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, d_backing_inode(root));
+ 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;
+}