selinux: handle files opened with flags 3 by checking ioctl permission

Handle files opened with flags 3 by checking ioctl permission.

Default to returning FILE__IOCTL from file_to_av() if the f_mode has neither
FMODE_READ nor FMODE_WRITE, and thus check ioctl permission on exec or
transfer, thereby validating such descriptors early as with normal r/w
descriptors and catching leaks of them prior to attempted usage.

Signed-off-by:  Stephen Smalley <[email protected]>
Acked-by: Eric Paris <[email protected]>
Signed-off-by: James Morris <[email protected]>

security/selinux/hooks.c

@@ -1630,6 +1630,12 @@ static inline u32 file_to_av(struct file *file)
 		else
 			av |= FILE__WRITE;
 	}
+	if (!av) {
+		/*
+		 * Special file opened with flags 3 for ioctl-only use.
+		 */
+		av = FILE__IOCTL;
+	}
 
 	return av;
 }