[natty, natty/ti-omap4 CVE 1/1] ipv6: make fragment identifications less predictable

Andy Whitcroft apw at canonical.com
Tue Aug 23 14:58:32 UTC 2011


[ 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 at gont.com.ar>
Signed-off-by: Eric Dumazet <eric.dumazet at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

CVE-2011-2699
BugLink: http://bugs.launchpad.net/bugs/827685
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 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 96e50e0..24175cf 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -460,17 +460,7 @@ 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 42a0eb6..70eef79 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 978e80e..ca171b7 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -1081,6 +1081,8 @@ 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 5f8d242..ed0c1a7 100644
--- 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;
@@ -1030,7 +1059,8 @@ 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;
@@ -1075,7 +1105,7 @@ 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);
 
@@ -1231,7 +1261,7 @@ 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 119edb6..b6de206 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1360,7 +1360,7 @@ 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()
-- 
1.7.4.1




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