[NETFILTER] nfnetlink: use highest bit of nfa_type to indicate nested TLV

As Henrik Nordstrom pointed out, all our efforts with "split endian" (i.e.
host byte order tags, net byte order values) are useless, unless a parser
can determine whether an attribute is nested or not.

This patch steals the highest bit of nfattr.nfa_type to indicate whether
the data payload contains a nested nfattr (1) or not (0).

This will break userspace compatibility, but luckily no kernel with
nfnetlink was released so far.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/include/linux/netfilter/nfnetlink.h b/include/linux/netfilter/nfnetlink.h
index 1d5b10ae2399..f08e870100f4 100644
--- a/include/linux/netfilter/nfnetlink.h
+++ b/include/linux/netfilter/nfnetlink.h
@@ -41,11 +41,15 @@ enum nfnetlink_groups {
 struct nfattr
 {
         u_int16_t nfa_len;
-        u_int16_t nfa_type;
+        u_int16_t nfa_type;     /* we use 15 bits for the type, and the highest
+                                 * bit to indicate whether the payload is nested */
 } __attribute__ ((packed));
 
-/* FIXME: Shamelessly copy and pasted from rtnetlink.h, it's time
- *        to put this in a generic file */
+/* FIXME: Apart from NFNL_NFA_NESTED shamelessly copy and pasted from
+ * rtnetlink.h, it's time to put this in a generic file */
+
+#define NFNL_NFA_NEST   0x8000
+#define NFA_TYPE(attr)  ((attr)->nfa_type & 0x7fff)
 
 #define NFA_ALIGNTO     4
 #define NFA_ALIGN(len)  (((len) + NFA_ALIGNTO - 1) & ~(NFA_ALIGNTO - 1))
@@ -59,7 +63,7 @@ struct nfattr
 #define NFA_PAYLOAD(nfa) ((int)((nfa)->nfa_len) - NFA_LENGTH(0))
 #define NFA_NEST(skb, type) \
 ({      struct nfattr *__start = (struct nfattr *) (skb)->tail; \
-        NFA_PUT(skb, type, 0, NULL); \
+        NFA_PUT(skb, (NFNL_NFA_NEST | type), 0, NULL); \
         __start;  })
 #define NFA_NEST_END(skb, start) \
 ({      (start)->nfa_len = ((skb)->tail - (unsigned char *) (start)); \