ima: provide flag to identify new empty files

On ima_file_free(), newly created empty files are not labeled with
an initial security.ima value, because the iversion did not change.
Commit dff6efc "fs: fix iversion handling" introduced a change in
iversion behavior. To verify this change use the shell command:

$ (exec >foo)
$ getfattr -h -e hex -d -m security foo

This patch defines the IMA_NEW_FILE flag. The flag is initially
set, when IMA detects that a new file is created, and subsequently
checked on the ima_file_free() hook to set the initial security.ima
value.

Signed-off-by: Dmitry Kasatkin <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>
Cc: <[e-mail]> 3.14+

security/integrity/ima/ima_appraise.c

···
 			goto out;
 
 		cause = "missing-hash";
-		status =
-		    (inode->i_size == 0) ? INTEGRITY_PASS : INTEGRITY_NOLABEL;
+		status = INTEGRITY_NOLABEL;
+		if (inode->i_size == 0) {
+			iint->flags |= IMA_NEW_FILE;
+			status = INTEGRITY_PASS;
+		}
 		goto out;
 	}
 

security/integrity/ima/ima_main.c

···
 		return;
 
 	mutex_lock(&inode->i_mutex);
-	if (atomic_read(&inode->i_writecount) == 1 &&
-	    iint->version != inode->i_version) {
-		iint->flags &= ~IMA_DONE_MASK;
-		if (iint->flags & IMA_APPRAISE)
-			ima_update_xattr(iint, file);
+	if (atomic_read(&inode->i_writecount) == 1) {
+		if ((iint->version != inode->i_version) ||
+		    (iint->flags & IMA_NEW_FILE)) {
+			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
+			if (iint->flags & IMA_APPRAISE)
+				ima_update_xattr(iint, file);
+		}
 	}
 	mutex_unlock(&inode->i_mutex);
 }

security/integrity/integrity.h

···
 #define IMA_DIGSIG		0x01000000
 #define IMA_DIGSIG_REQUIRED	0x02000000
 #define IMA_PERMIT_DIRECTIO	0x04000000
+#define IMA_NEW_FILE		0x08000000
 
 #define IMA_DO_MASK		(IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
 				 IMA_APPRAISE_SUBMASK)