Patch for 3.2.x, 3.4.x IP identifier regression

commit c3b4ccb8b03769e2867fabecc078483ee6710ccf upstream.

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@cs.unm.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Eric Dumazet <edumazet@google.com>
[Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 7827436..330be87 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1346,10 +1346,10 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
        iph->ihl = 5;
        iph->tos = inet->tos;
        iph->frag_off = df;
-       ip_select_ident(skb, sk);
        iph->ttl = ttl;
        iph->protocol = sk->sk_protocol;
        ip_copy_addrs(iph, fl4);
+       ip_select_ident(skb, sk);
 
        if (opt) {
                iph->ihl += opt->optlen>>2;