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authorDavid Howells <dhowells@redhat.com>2021-11-26 14:59:10 +0000
committerDavid Howells <dhowells@redhat.com>2022-01-07 13:41:14 +0000
commit254947d47945f2fa02e9b3366594fad2ed127618 (patch)
treeb65de1ad1bcbbc7bfe9aefccff113b9285d2cdf0 /fs/cachefiles
parent1493bf74bcf2434a840eacef60c0f56966faa11a (diff)
cachefiles: Add security derivation
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
Diffstat (limited to 'fs/cachefiles')
-rw-r--r--fs/cachefiles/Makefile3
-rw-r--r--fs/cachefiles/internal.h20
-rw-r--r--fs/cachefiles/security.c112
3 files changed, 134 insertions, 1 deletions
diff --git a/fs/cachefiles/Makefile b/fs/cachefiles/Makefile
index 183fb5f3b8b1..28bbb0d14868 100644
--- a/fs/cachefiles/Makefile
+++ b/fs/cachefiles/Makefile
@@ -4,7 +4,8 @@
#
cachefiles-y := \
- main.o
+ main.o \
+ security.o
cachefiles-$(CONFIG_CACHEFILES_ERROR_INJECTION) += error_inject.o
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index b2adcb59b4ce..e57ce5ef875c 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -105,6 +105,26 @@ static inline int cachefiles_inject_remove_error(void)
}
/*
+ * security.c
+ */
+extern int cachefiles_get_security_ID(struct cachefiles_cache *cache);
+extern int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
+ struct dentry *root,
+ const struct cred **_saved_cred);
+
+static inline void cachefiles_begin_secure(struct cachefiles_cache *cache,
+ const struct cred **_saved_cred)
+{
+ *_saved_cred = override_creds(cache->cache_cred);
+}
+
+static inline void cachefiles_end_secure(struct cachefiles_cache *cache,
+ const struct cred *saved_cred)
+{
+ revert_creds(saved_cred);
+}
+
+/*
* Error handling
*/
#define cachefiles_io_error(___cache, FMT, ...) \
diff --git a/fs/cachefiles/security.c b/fs/cachefiles/security.c
new file mode 100644
index 000000000000..fe777164f1d8
--- /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;
+}