tty: Fix copying of termios character map

The system termios structure and our PB
equivalent defined quite different, while
first defined as plain array we use dynamically
allocated memory. Thus the use of min() macro
is incorrect here and always produce the size of
pointer.

Fix it using the size of array from the system
provided structure. The BUILD_BUG_ON will prevent
from accidental changes.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

tty.c

@@ -122,9 +122,10 @@ int prepare_shared_tty(void)
 
 #define termios_copy(d, s)				\
 	do {						\
+		struct termios __t;			\
+							\
 		memcpy((d)->c_cc, (s)->c_cc,		\
-		       min(sizeof((s)->c_cc),		\
-			   sizeof((d)->c_cc)));		\
+		       sizeof(__t.c_cc));		\
 							\
 		ASSIGN_MEMBER((d),(s), c_iflag);	\
 		ASSIGN_MEMBER((d),(s), c_oflag);	\
@@ -927,6 +928,14 @@ static int dump_pty_info(int lfd, u32 id, const struct fd_parms *p, int major, i
 
 	int ret = -1, sid, pgrp;
 
+	/*
+	 * Make sure the structures the system provides us
+	 * correlates well with protobuf templates.
+	 */
+	BUILD_BUG_ON(ARRAY_SIZE(t.c_cc) < TERMIOS_NCC);
+	BUILD_BUG_ON(sizeof(termios.c_cc) != sizeof(void *));
+	BUILD_BUG_ON((sizeof(termios.c_cc) * TERMIOS_NCC) < sizeof(t.c_cc));
+
 	if (tty_get_sid_pgrp(lfd, &sid, &pgrp, &hangup))
 		return -1;