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Date: Wed, 20 Jul 2011 12:27:28 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Fernando Gont <fernando@...t.com.ar>,
David Miller <davem@...emloft.net>
Cc: security@...nel.org, Eugene Teo <eugeneteo@...nel.sg>,
netdev <netdev@...r.kernel.org>, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH net-next-2.6] ipv6: make fragment identifications less
predictable
Le mercredi 20 juillet 2011 à 10:25 +0200, Eric Dumazet a écrit :
> Please hold on, I'll make a different patch series to ease stable teams
> job. It appears inetpeer & ipv6 are really not an option for old
> kernels.
>
> Common patch for all kernels :
> 1) Fix the problem without inetpeer help
> ---
> Patches for next kernels
> 2) random split as suggested by Matt Mackal
> 3) Use inetpeer cache to scale identification generation
>
Here is the first patch, applicable on net-2.6 / linux-2.6 and stable
kernels.
Thanks
[PATCH v2] ipv6: make fragment identifications less predictable
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@...t.com.ar>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Matt Mackall <mpm@...enic.com>
CC: Eugene Teo <eugeneteo@...nel.sg>
---
include/net/ipv6.h | 12 -----------
net/ipv6/ip6_output.c | 43 +++++++++++++++++++++++++++++++++++-----
net/ipv6/udp.c | 2 -
3 files changed, 40 insertions(+), 17 deletions(-)
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index c033ed0..3b5ac1f 100644
--- 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/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 9d4b165..8a444c8 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -596,6 +596,38 @@ 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];
+
+static int __init initialize_hashidentrnd(void)
+{
+ get_random_bytes(&hashidentrnd, sizeof(hashidentrnd));
+ return 0;
+}
+
+late_initcall_sync(initialize_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 +712,7 @@ 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 +858,7 @@ 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 +1104,8 @@ 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 +1149,7 @@ 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 +1315,7 @@ 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 328985c..29213b5 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()
--
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