[NETLINK]: introduce NLA_BINARY type

This patch introduces a new NLA_BINARY attribute policy type with the
verification of simply checking the maximum length of the payload.

It also fixes a small typo in the example.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NThomas Graf <tgraf@suug.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -171,6 +171,7 @@ enum {
 	NLA_MSECS,
 	NLA_NESTED,
 	NLA_NUL_STRING,
+	NLA_BINARY,
 	__NLA_TYPE_MAX,
 };
 
@@ -188,12 +189,13 @@ enum {
  *    NLA_STRING           Maximum length of string
  *    NLA_NUL_STRING       Maximum length of string (excluding NUL)
  *    NLA_FLAG             Unused
+ *    NLA_BINARY           Maximum length of attribute payload
  *    All other            Exact length of attribute payload
  *
  * Example:
  * static struct nla_policy my_policy[ATTR_MAX+1] __read_mostly = {
  * 	[ATTR_FOO] = { .type = NLA_U16 },
- *	[ATTR_BAR] = { .type = NLA_STRING, len = BARSIZ },
+ *	[ATTR_BAR] = { .type = NLA_STRING, .len = BARSIZ },
  *	[ATTR_BAZ] = { .len = sizeof(struct mystruct) },
  * };
  */

net/netlink/attr.c

@@ -67,6 +67,11 @@ static int validate_nla(struct nlattr *nla, int maxtype,
 		}
 		break;
 
+	case NLA_BINARY:
+		if (pt->len && attrlen > pt->len)
+			return -ERANGE;
+		break;
+
 	default:
 		if (pt->len)
 			minlen = pt->len;