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, 32 insertions, 6 deletions

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()