ipv6: make fragment identifications less predictable

[ Backport of upstream commit 87c48fa3b4630905f98268dde838ee43626a060c ]

Fernando Gont reported current IPv6 fragment identification generation
was not secure, because using a very predictable system-wide generator,
allowing various attacks.

IPv4 uses inetpeer cache to address this problem and to get good
performance. We'll use this mechanism when IPv6 inetpeer is stable
enough in linux-3.1

For the time being, we use jhash on destination address to provide less
predictable identifications. Also remove a spinlock and use cmpxchg() to
get better SMP performance.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index c033ed00df7da0e22a0735bbcf791e30c05cf486..3b5ac1fbff39f50c51e55b07bd743172d1a9e0e5 100644 (file)
--- 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

diff --git a/include/net/transp_v6.h b/include/net/transp_v6.h
index 5271a741c3a3f6c54b0bc7ec2cf78d53f8578eaa..45ce307e954ed4c2c70d5cee12eaf87ae6820efb 100644 (file)
--- a/include/net/transp_v6.h
+++ b/include/net/transp_v6.h
@@ -14,6 +14,8 @@ extern struct proto tcpv6_prot;
 
 struct flowi6;
 
+extern void initialize_hashidentrnd(void);
+
 /* extension headers */
 extern int                             ipv6_exthdrs_init(void);
 extern void                            ipv6_exthdrs_exit(void);

diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 3b5669a2582df03c1f1b896991fba664e137d62e..559123644e5d8c6c698437eb172a82153934dcb6 100644 (file)
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -1078,6 +1078,8 @@ static int __init inet6_init(void)
                goto out;
        }
 
+       initialize_hashidentrnd();
+
        err = proto_register(&tcpv6_prot, 1);
        if (err)
                goto out;

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 9d4b165837d6abff686c729967aec4534d435feb..16612968aaaf2f36959d49d10642b204f3778ce5 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -596,6 +596,35 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
        return offset;
 }
 
+static u32 hashidentrnd __read_mostly;
+#define FID_HASH_SZ 16
+static u32 ipv6_fragmentation_id[FID_HASH_SZ];
+
+void __init initialize_hashidentrnd(void)
+{
+       get_random_bytes(&hashidentrnd, sizeof(hashidentrnd));
+}
+
+static u32 __ipv6_select_ident(const struct in6_addr *addr)
+{
+       u32 newid, oldid, hash = jhash2((u32 *)addr, 4, hashidentrnd);
+       u32 *pid = &ipv6_fragmentation_id[hash % FID_HASH_SZ];
+
+       do {
+               oldid = *pid;
+               newid = oldid + 1;
+               if (!(hash + newid))
+                       newid++;
+       } while (cmpxchg(pid, oldid, newid) != oldid);
+
+       return hash + newid;
+}
+
+void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
+{
+       fhdr->identification = htonl(__ipv6_select_ident(&rt->rt6i_dst.addr));
+}
+
 int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 {
        struct sk_buff *frag;
@@ -680,7 +709,7 @@ 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 +855,7 @@ 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;
@@ -1072,7 +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;
@@ -1116,7 +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);
 
@@ -1282,7 +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 328985c408838ad9e50fb1e209cc4f9c592a56a3..29213b51c4998e09a79f60fd534015269da54570 100644 (file)
--- 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()