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/include/linux/cred.h b/include/linux/cred.h
index 55a9c99..26c1ab1 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -18,6 +18,7 @@
struct user_struct;
struct cred;
+struct inode;
/*
* COW Supplementary groups list
@@ -148,6 +149,11 @@
extern void abort_creds(struct cred *);
extern const struct cred *override_creds(const struct cred *);
extern void revert_creds(const struct cred *);
+extern struct cred *prepare_kernel_cred(struct task_struct *);
+extern int change_create_files_as(struct cred *, struct inode *);
+extern int set_security_override(struct cred *, u32);
+extern int set_security_override_from_ctx(struct cred *, const char *);
+extern int set_create_files_as(struct cred *, struct inode *);
extern void __init cred_init(void);
/**
diff --git a/include/linux/security.h b/include/linux/security.h
index 56a0eed..59a11e1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -587,6 +587,19 @@
* @new points to the new credentials.
* @old points to the original credentials.
* Install a new set of credentials.
+ * @kernel_act_as:
+ * Set the credentials for a kernel service to act as (subjective context).
+ * @new points to the credentials to be modified.
+ * @secid specifies the security ID to be set
+ * The current task must be the one that nominated @secid.
+ * Return 0 if successful.
+ * @kernel_create_files_as:
+ * Set the file creation context in a set of credentials to be the same as
+ * the objective context of the specified inode.
+ * @new points to the credentials to be modified.
+ * @inode points to the inode to use as a reference.
+ * The current task must be the one that nominated @inode.
+ * Return 0 if successful.
* @task_setuid:
* Check permission before setting one or more of the user identity
* attributes of the current process. The @flags parameter indicates
@@ -1381,6 +1394,8 @@
int (*cred_prepare)(struct cred *new, const struct cred *old,
gfp_t gfp);
void (*cred_commit)(struct cred *new, const struct cred *old);
+ int (*kernel_act_as)(struct cred *new, u32 secid);
+ int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
int (*task_setuid) (uid_t id0, uid_t id1, uid_t id2, int flags);
int (*task_fix_setuid) (struct cred *new, const struct cred *old,
int flags);
@@ -1632,6 +1647,8 @@
void security_cred_free(struct cred *cred);
int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
void security_commit_creds(struct cred *new, const struct cred *old);
+int security_kernel_act_as(struct cred *new, u32 secid);
+int security_kernel_create_files_as(struct cred *new, struct inode *inode);
int security_task_setuid(uid_t id0, uid_t id1, uid_t id2, int flags);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags);
@@ -2151,6 +2168,17 @@
{
}
+static inline int security_kernel_act_as(struct cred *cred, u32 secid)
+{
+ return 0;
+}
+
+static inline int security_kernel_create_files_as(struct cred *cred,
+ struct inode *inode)
+{
+ return 0;
+}
+
static inline int security_task_setuid(uid_t id0, uid_t id1, uid_t id2,
int flags)
{