Integrity: IMA file free imbalance

The number of calls to ima_path_check()/ima_file_free()
should be balanced.  An extra call to fput(), indicates
the file could have been accessed without first being
measured.

Although f_count is incremented/decremented in places other
than fget/fput, like fget_light/fput_light and get_file, the
current task must already hold a file refcnt.  The call to
__fput() is delayed until the refcnt becomes 0, resulting
in ima_file_free() flagging any changes.

- add hook to increment opencount for IPC shared memory(SYSV),
  shmat files, and /dev/zero
- moved NULL iint test in opencount_get()

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/integrity/ima/ima.h

@@ -97,6 +97,7 @@ static inline unsigned long ima_hash_key(u8 *digest)
 
 /* iint cache flags */
 #define IMA_MEASURED		1
+#define IMA_IINT_DUMP_STACK	512
 
 /* integrity data associated with an inode */
 struct ima_iint_cache {
@@ -106,6 +107,7 @@ struct ima_iint_cache {
 	struct mutex mutex;	/* protects: version, flags, digest */
 	long readcount;		/* measured files readcount */
 	long writecount;	/* measured files writecount */
+	long opencount;		/* opens reference count */
 	struct kref refcount;	/* ima_iint_cache reference count */
 	struct rcu_head rcu;
 };