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>

3 files changed, 37 insertions, 8 deletions

diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 90c5f0d1bcf3..e38213817d0a 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -391,7 +391,7 @@ static int inet_peer_gc(struct inet_peer_base *base,
 	return cnt;
 }
 
-struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
+struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create)
 {
 	struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
 	struct inet_peer_base *base = family_to_base(daddr->family);
@@ -436,7 +436,10 @@ relookup:
 		p->daddr = *daddr;
 		atomic_set(&p->refcnt, 1);
 		atomic_set(&p->rid, 0);
-		atomic_set(&p->ip_id_count, secure_ip_id(daddr->addr.a4));
+		atomic_set(&p->ip_id_count,
+				(daddr->family == AF_INET) ?
+					secure_ip_id(daddr->addr.a4) :
+					secure_ipv6_id(daddr->addr.a6));
 		p->tcp_ts_stamp = 0;
 		p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
 		p->rate_tokens = 0;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 8db0e4875ad8..32e5339db0c8 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -596,6 +596,31 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 	return offset;
 }
 
+void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
+{
+	static atomic_t ipv6_fragmentation_id;
+	int old, new;
+
+	if (rt) {
+		struct inet_peer *peer;
+
+		if (!rt->rt6i_peer)
+			rt6_bind_peer(rt, 1);
+		peer = rt->rt6i_peer;
+		if (peer) {
+			fhdr->identification = htonl(inet_getid(peer, 0));
+			return;
+		}
+	}
+	do {
+		old = atomic_read(&ipv6_fragmentation_id);
+		new = old + 1;
+		if (!new)
+			new = 1;
+	} while (atomic_cmpxchg(&ipv6_fragmentation_id, old, new) != old);
+	fhdr->identification = htonl(new);
+}
+
 int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 {
 	struct sk_buff *frag;
@@ -680,7 +705,7 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 		skb_reset_network_header(skb);
 		memcpy(skb_network_header(skb), tmp_hdr, hlen);
 
-		ipv6_select_ident(fh);
+		ipv6_select_ident(fh, rt);
 		fh->nexthdr = nexthdr;
 		fh->reserved = 0;
 		fh->frag_off = htons(IP6_MF);
@@ -826,7 +851,7 @@ slow_path:
 		fh->nexthdr = nexthdr;
 		fh->reserved = 0;
 		if (!frag_id) {
-			ipv6_select_ident(fh);
+			ipv6_select_ident(fh, rt);
 			frag_id = fh->identification;
 		} else
 			fh->identification = frag_id;
@@ -1076,7 +1101,8 @@ static inline int ip6_ufo_append_data(struct sock *sk,
 			int getfrag(void *from, char *to, int offset, int len,
 			int odd, struct sk_buff *skb),
 			void *from, int length, int hh_len, int fragheaderlen,
-			int transhdrlen, int mtu,unsigned int flags)
+			int transhdrlen, int mtu,unsigned int flags,
+			struct rt6_info *rt)
 
 {
 	struct sk_buff *skb;
@@ -1120,7 +1146,7 @@ static inline int ip6_ufo_append_data(struct sock *sk,
 		skb_shinfo(skb)->gso_size = (mtu - fragheaderlen -
 					     sizeof(struct frag_hdr)) & ~7;
 		skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
-		ipv6_select_ident(&fhdr);
+		ipv6_select_ident(&fhdr, rt);
 		skb_shinfo(skb)->ip6_frag_id = fhdr.identification;
 		__skb_queue_tail(&sk->sk_write_queue, skb);
 
@@ -1286,7 +1312,7 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
 
 			err = ip6_ufo_append_data(sk, getfrag, from, length,
 						  hh_len, fragheaderlen,
-						  transhdrlen, mtu, flags);
+						  transhdrlen, mtu, flags, rt);
 			if (err)
 				goto error;
 			return 0;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 328985c40883..29213b51c499 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1359,7 +1359,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb, u32 features)
 	fptr = (struct frag_hdr *)(skb_network_header(skb) + unfrag_ip6hlen);
 	fptr->nexthdr = nexthdr;
 	fptr->reserved = 0;
-	ipv6_select_ident(fptr);
+	ipv6_select_ident(fptr, (struct rt6_info *)skb_dst(skb));
 
 	/* Fragment the skb. ipv6 header and the remaining fields of the
 	 * fragment header are updated in ipv6_gso_segment()