keys: add keyctl function to get a security label

Add a keyctl() function to get the security label of a key.

The following is added to Documentation/keys.txt:

 (*) Get the LSM security context attached to a key.

	long keyctl(KEYCTL_GET_SECURITY, key_serial_t key, char *buffer,
		    size_t buflen)

     This function returns a string that represents the LSM security context
     attached to a key in the buffer provided.

     Unless there's an error, it always returns the amount of data it could
     produce, even if that's too big for the buffer, but it won't copy more
     than requested to userspace. If the buffer pointer is NULL then no copy
     will take place.

     A NUL character is included at the end of the string if the buffer is
     sufficiently big.  This is included in the returned count.  If no LSM is
     in force then an empty string will be returned.

     A process must have view permission on the key for this function to be
     successful.

[akpm@linux-foundation.org: declare keyctl_get_security()]
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Paul Moore <paul.moore@hp.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: James Morris <jmorris@namei.org>
Cc: Kevin Coffman <kwc@citi.umich.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 20 insertions, 1 deletions

diff --git a/include/linux/keyctl.h b/include/linux/keyctl.h
index 3365945640c9..656ee6b77a4a 100644
--- a/include/linux/keyctl.h
+++ b/include/linux/keyctl.h
@@ -49,5 +49,6 @@
 #define KEYCTL_SET_REQKEY_KEYRING	14	/* set default request-key keyring */
 #define KEYCTL_SET_TIMEOUT		15	/* set key timeout */
 #define KEYCTL_ASSUME_AUTHORITY		16	/* assume request_key() authorisation */
+#define KEYCTL_GET_SECURITY		17	/* get key security label */
 
 #endif /*  _LINUX_KEYCTL_H */
diff --git a/include/linux/security.h b/include/linux/security.h
index 3ebcdd00b17d..adb09d893ae0 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1009,6 +1009,17 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *	@perm describes the combination of permissions required of this key.
  *	Return 1 if permission granted, 0 if permission denied and -ve it the
  *	normal permissions model should be effected.
+ * @key_getsecurity:
+ *	Get a textual representation of the security context attached to a key
+ *	for the purposes of honouring KEYCTL_GETSECURITY.  This function
+ *	allocates the storage for the NUL-terminated string and the caller
+ *	should free it.
+ *	@key points to the key to be queried.
+ *	@_buffer points to a pointer that should be set to point to the
+ *	 resulting string (if no label or an error occurs).
+ *	Return the length of the string (including terminating NUL) or -ve if
+ *      an error.
+ *	May also return 0 (and a NULL buffer pointer) if there is no label.
  *
  * Security hooks affecting all System V IPC operations.
  *
@@ -1538,7 +1549,7 @@ struct security_operations {
 	int (*key_permission) (key_ref_t key_ref,
 			       struct task_struct *context,
 			       key_perm_t perm);
-
+	int (*key_getsecurity)(struct key *key, char **_buffer);
 #endif	/* CONFIG_KEYS */
 
 #ifdef CONFIG_AUDIT
@@ -2732,6 +2743,7 @@ int security_key_alloc(struct key *key, struct task_struct *tsk, unsigned long f
 void security_key_free(struct key *key);
 int security_key_permission(key_ref_t key_ref,
 			    struct task_struct *context, key_perm_t perm);
+int security_key_getsecurity(struct key *key, char **_buffer);
 
 #else
 
@@ -2753,6 +2765,12 @@ static inline int security_key_permission(key_ref_t key_ref,
 	return 0;
 }
 
+static inline int security_key_getsecurity(struct key *key, char **_buffer)
+{
+	*_buffer = NULL;
+	return 0;
+}
+
 #endif
 #endif /* CONFIG_KEYS */