ipv6: make fragment identifications less predictable

IPv6 fragment identification generation is way beyond what we use for
IPv4 : It uses a single generator. Its not scalable and allows DOS
attacks.

Now inetpeer is IPv6 aware, we can use it to provide a more secure and
scalable frag ident generator (per destination, instead of system wide)

This patch :
1) defines a new secure_ipv6_id() helper
2) extends inet_getid() to provide 32bit results
3) extends ipv6_select_ident() with a new dest parameter

Reported-by: Fernando Gont <fernando@gont.com.ar>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 11 insertions, 14 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 39d1230..4233e6f 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -71,7 +71,7 @@ static inline bool inet_metrics_new(const struct inet_peer *p)
 }
 
 /* can be called with or without local BH being disabled */
-struct inet_peer	*inet_getpeer(struct inetpeer_addr *daddr, int create);
+struct inet_peer	*inet_getpeer(const struct inetpeer_addr *daddr, int create);
 
 static inline struct inet_peer *inet_getpeer_v4(__be32 v4daddr, int create)
 {
@@ -106,11 +106,18 @@ static inline void inet_peer_refcheck(const struct inet_peer *p)
 
 
 /* can be called with or without local BH being disabled */
-static inline __u16	inet_getid(struct inet_peer *p, int more)
+static inline int inet_getid(struct inet_peer *p, int more)
 {
+	int old, new;
 	more++;
 	inet_peer_refcheck(p);
-	return atomic_add_return(more, &p->ip_id_count) - more;
+	do {
+		old = atomic_read(&p->ip_id_count);
+		new = old + more;
+		if (!new)
+			new = 1;
+	} while (atomic_cmpxchg(&p->ip_id_count, old, new) != old);
+	return new;
 }
 
 #endif /* _NET_INETPEER_H */
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index c033ed0..3b5ac1f 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -463,17 +463,7 @@ static inline int ipv6_addr_diff(const struct in6_addr *a1, const struct in6_add
 	return __ipv6_addr_diff(a1, a2, sizeof(struct in6_addr));
 }
 
-static __inline__ void ipv6_select_ident(struct frag_hdr *fhdr)
-{
-	static u32 ipv6_fragmentation_id = 1;
-	static DEFINE_SPINLOCK(ip6_id_lock);
-
-	spin_lock_bh(&ip6_id_lock);
-	fhdr->identification = htonl(ipv6_fragmentation_id);
-	if (++ipv6_fragmentation_id == 0)
-		ipv6_fragmentation_id = 1;
-	spin_unlock_bh(&ip6_id_lock);
-}
+extern void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt);
 
 /*
  *	Prototypes exported by ipv6