[PATCH 3.2 162/164] Patch for 3.2.x, 3.4.x IP identifier regression

From: Ben Hutchings
Date: Fri Dec 12 2014 - 02:02:09 EST

3.2.65-rc1 review patch. If anyone has any objections, please let me know.


From: Jeffrey Knockel <jeffk@xxxxxxxxxx>

With commits 73f156a6e8c1 ("inetpeer: get rid of ip_id_count") and
04ca6973f7c1 ("ip: make IP identifiers less predictable"), IP
identifiers are generated from a counter chosen from an array of
counters indexed by the hash of the outgoing packet header's source
address, destination address, and protocol number. Thus, in
__ip_make_skb(), we must now call ip_select_ident() only after setting
these fields in the IP header to prevent IP identifiers from being
generated from bogus counters.

IP id sequence before fix: 18174, 5789, 5953, 59420, 59637, ...
After fix: 5967, 6185, 6374, 6600, 6795, 6892, 7051, 7288, ...

Signed-off-by: Jeffrey Knockel <jeffk@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1333,11 +1333,11 @@ struct sk_buff *__ip_make_skb(struct soc
iph->ihl = 5;
iph->tos = inet->tos;
iph->frag_off = df;
- ip_select_ident(skb, sk);
iph->ttl = ttl;
iph->protocol = sk->sk_protocol;
iph->saddr = fl4->saddr;
iph->daddr = fl4->daddr;
+ ip_select_ident(skb, sk);

if (opt) {
iph->ihl += opt->optlen>>2;

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