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/selinux/hooks.c b/security/selinux/hooks.c
index 91b06f2..520f82a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3277,6 +3277,50 @@
secondary_ops->cred_commit(new, old);
}
+/*
+ * set the security data for a kernel service
+ * - all the creation contexts are set to unlabelled
+ */
+static int selinux_kernel_act_as(struct cred *new, u32 secid)
+{
+ struct task_security_struct *tsec = new->security;
+ u32 sid = current_sid();
+ int ret;
+
+ ret = avc_has_perm(sid, secid,
+ SECCLASS_KERNEL_SERVICE,
+ KERNEL_SERVICE__USE_AS_OVERRIDE,
+ NULL);
+ if (ret == 0) {
+ tsec->sid = secid;
+ tsec->create_sid = 0;
+ tsec->keycreate_sid = 0;
+ tsec->sockcreate_sid = 0;
+ }
+ return ret;
+}
+
+/*
+ * set the file creation context in a security record to the same as the
+ * objective context of the specified inode
+ */
+static int selinux_kernel_create_files_as(struct cred *new, struct inode *inode)
+{
+ struct inode_security_struct *isec = inode->i_security;
+ struct task_security_struct *tsec = new->security;
+ u32 sid = current_sid();
+ int ret;
+
+ ret = avc_has_perm(sid, isec->sid,
+ SECCLASS_KERNEL_SERVICE,
+ KERNEL_SERVICE__CREATE_FILES_AS,
+ NULL);
+
+ if (ret == 0)
+ tsec->create_sid = isec->sid;
+ return 0;
+}
+
static int selinux_task_setuid(uid_t id0, uid_t id1, uid_t id2, int flags)
{
/* Since setuid only affects the current process, and
@@ -5593,6 +5637,8 @@
.cred_free = selinux_cred_free,
.cred_prepare = selinux_cred_prepare,
.cred_commit = selinux_cred_commit,
+ .kernel_act_as = selinux_kernel_act_as,
+ .kernel_create_files_as = selinux_kernel_create_files_as,
.task_setuid = selinux_task_setuid,
.task_fix_setuid = selinux_task_fix_setuid,
.task_setgid = selinux_task_setgid,