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Subject[ 168/184] ipv6: make fragment identifications less predictable
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <eric.dumazet@gmail.com>

[ 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 | 12 +-----------
include/net/transp_v6.h | 2 ++
net/ipv6/af_inet6.c | 2 ++
net/ipv6/ip6_output.c | 40 +++++++++++++++++++++++++++++++++++-----
net/ipv6/udp.c | 2 +-
5 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 639bbf0..52d86da 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -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
diff --git a/include/net/transp_v6.h b/include/net/transp_v6.h
index d65381c..8beefe1 100644
--- a/include/net/transp_v6.h
+++ b/include/net/transp_v6.h
@@ -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);
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index e127a32..835590d 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -1073,6 +1073,8 @@ 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 9ad5792..6ba0fe2 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -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;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 9cc6289..d8c0374 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -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()
--
1.7.12.2.21.g234cd45.dirty




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