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@xxxxxxxxxx> cc: linux-cachefs@xxxxxxxxxx Link: https://lore.kernel.org/r/163819627469.215744.3603633690679962985.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1 --- fs/cachefiles/Makefile | 3 + fs/cachefiles/internal.h | 20 ++++++++ fs/cachefiles/security.c | 112 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 134 insertions(+), 1 deletion(-) create mode 100644 fs/cachefiles/security.c 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 @@ -104,6 +104,26 @@ static inline int cachefiles_inject_remove_error(void) return cachefiles_error_injection_state & 2 ? -EIO : 0; } +/* + * 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 */ 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@xxxxxxxxxx) + */ + +#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; +}
