ipv6: make fragment identifications less predictable
authorEric Dumazet <eric.dumazet@gmail.com>
Tue, 9 Aug 2011 06:44:00 +0000 (23:44 -0700)
committerWilly Tarreau <w@1wt.eu>
Mon, 10 Jun 2013 09:43:37 +0000 (11:43 +0200)
[ 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>
[bwh: Backport further to 2.6.32]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Willy Tarreau <w@1wt.eu>
include/net/ipv6.h
include/net/transp_v6.h
net/ipv6/af_inet6.c
net/ipv6/ip6_output.c
net/ipv6/udp.c

index 639bbf06d378cdbb0c480ac9a564add0235ca688..52d86dabefa0e819e128ca8ab4f10320cefdccc2 100644 (file)
@@ -449,17 +449,7 @@ 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
index d65381cad0fcc5298bbb1a879afb6afc3b7e3345..8beefe1d0a402c55e5723d4f96206ef39d318f46 100644 (file)
@@ -16,6 +16,8 @@ extern struct proto tcpv6_prot;
 
 struct flowi;
 
+extern void initialize_hashidentrnd(void);
+
 /* extention headers */
 extern int                             ipv6_exthdrs_init(void);
 extern void                            ipv6_exthdrs_exit(void);
index e127a32f9540fecfaee5de6332ca1be64ce6541f..835590d68876b1e3d55b6d717b98528b649a4aad 100644 (file)
@@ -1073,6 +1073,8 @@ static int __init inet6_init(void)
                goto out;
        }
 
+       initialize_hashidentrnd();
+
        err = proto_register(&tcpv6_prot, 1);
        if (err)
                goto out;
index 9ad57923440f4dee631eb14b9e502c03858aa551..6ba0fe27baf0f91287ed5740597669bee3728626 100644 (file)
@@ -604,6 +604,35 @@ 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));
+}
+
 static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 {
        struct sk_buff *frag;
@@ -689,7 +718,7 @@ static 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);
@@ -835,7 +864,7 @@ 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;
@@ -1039,7 +1068,8 @@ 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;
@@ -1084,7 +1114,7 @@ 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);
 
@@ -1233,7 +1263,7 @@ 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);
+                                         flags, rt);
                if (err)
                        goto error;
                return 0;
index 9cc6289acaedb235ee93187ec95b8845d202f888..d8c0374400784115b86236d441d21b28953c29b3 100644 (file)
@@ -1162,7 +1162,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb, int 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()