net neighbour, decnet: Ensure to align device private data on preferred alignment.

To allow both of protocol-specific data and device-specific data
attached with neighbour entry, and to eliminate size calculation
cost when allocating entry, sizeof protocol-speicic data must be
multiple of NEIGH_PRIV_ALIGN. On 64bit archs,
sizeof(struct dn_neigh) is multiple of NEIGH_PRIV_ALIGN, but on
32bit archs, it was not.

Introduce NEIGH_ENTRY_SPACE() macro to ensure that protocol-specific
entry-size meets our requirement.

Reported-by: Fengguang Wu <[e-mail]>
Signed-off-by: YOSHIFUJI Hideaki <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/neighbour.h

···
 };
 
 #define NEIGH_PRIV_ALIGN	sizeof(long long)
+#define NEIGH_ENTRY_SIZE(size)	ALIGN((size), NEIGH_PRIV_ALIGN)
 
 static inline void *neighbour_priv(const struct neighbour *n)
 {

net/decnet/dn_neigh.c

···
 
 struct neigh_table dn_neigh_table = {
 	.family =			PF_DECnet,
-	.entry_size =			sizeof(struct dn_neigh),
+	.entry_size =			NEIGH_ENTRY_SIZE(sizeof(struct dn_neigh)),
 	.key_len =			sizeof(__le16),
 	.hash =				dn_neigh_hash,
 	.constructor =			dn_neigh_construct,