CRED: Allow kernel services to override LSM settings for task actions
Allow kernel services to override LSM settings appropriate to the actions
performed by a task by duplicating a set of credentials, modifying it and then
using task_struct::cred to point to it when performing operations on behalf of
a task.
This is used, for example, by CacheFiles which has to transparently access the
cache on behalf of a process that thinks it is doing, say, NFS accesses with a
potentially inappropriate (with respect to accessing the cache) set of
credentials.
This patch provides two LSM hooks for modifying a task security record:
(*) security_kernel_act_as() which allows modification of the security datum
with which a task acts on other objects (most notably files).
(*) security_kernel_create_files_as() which allows modification of the
security datum that is used to initialise the security data on a file that
a task creates.
The patch also provides four new credentials handling functions, which wrap the
LSM functions:
(1) prepare_kernel_cred()
Prepare a set of credentials for a kernel service to use, based either on
a daemon's credentials or on init_cred. All the keyrings are cleared.
(2) set_security_override()
Set the LSM security ID in a set of credentials to a specific security
context, assuming permission from the LSM policy.
(3) set_security_override_from_ctx()
As (2), but takes the security context as a string.
(4) set_create_files_as()
Set the file creation LSM security ID in a set of credentials to be the
same as that on a particular inode.
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> [Smack changes]
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index de39674..8ad48161 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1012,6 +1012,41 @@
}
/**
+ * smack_kernel_act_as - Set the subjective context in a set of credentials
+ * @new points to the set of credentials to be modified.
+ * @secid specifies the security ID to be set
+ *
+ * Set the security data for a kernel service.
+ */
+static int smack_kernel_act_as(struct cred *new, u32 secid)
+{
+ char *smack = smack_from_secid(secid);
+
+ if (smack == NULL)
+ return -EINVAL;
+
+ new->security = smack;
+ return 0;
+}
+
+/**
+ * smack_kernel_create_files_as - Set the file creation label in a set of creds
+ * @new points to the set of credentials to be modified
+ * @inode points to the inode to use as a reference
+ *
+ * Set the file creation context in a set of credentials to the same
+ * as the objective context of the specified inode
+ */
+static int smack_kernel_create_files_as(struct cred *new,
+ struct inode *inode)
+{
+ struct inode_smack *isp = inode->i_security;
+
+ new->security = isp->smk_inode;
+ return 0;
+}
+
+/**
* smack_task_setpgid - Smack check on setting pgid
* @p: the task object
* @pgid: unused
@@ -2641,6 +2676,8 @@
.cred_free = smack_cred_free,
.cred_prepare = smack_cred_prepare,
.cred_commit = smack_cred_commit,
+ .kernel_act_as = smack_kernel_act_as,
+ .kernel_create_files_as = smack_kernel_create_files_as,
.task_fix_setuid = cap_task_fix_setuid,
.task_setpgid = smack_task_setpgid,
.task_getpgid = smack_task_getpgid,