ipv6: properly combine dev_base_seq and ipv6.dev_addr_genid

[ Upstream commit e898e4cd1aab271ca414f9ac6e08e4c761f6913c ]

net->dev_base_seq and ipv6.dev_addr_genid are monotonically increasing.

If we XOR their values, we could miss to detect if both values
were changed with the same amount.

Fixes: 63998ac24f83 ("ipv6: provide addr and netconf dump consistency info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index b007d098ffe2e124942c3b5f018b3ef664ac4002..7881446a46c4f743f05ef5f9fe29c6838c9842ee 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -706,6 +706,22 @@ errout:
        return err;
 }
 
+/* Combine dev_addr_genid and dev_base_seq to detect changes.
+ */
+static u32 inet6_base_seq(const struct net *net)
+{
+       u32 res = atomic_read(&net->ipv6.dev_addr_genid) +
+                 net->dev_base_seq;
+
+       /* Must not return 0 (see nl_dump_check_consistent()).
+        * Chose a value far away from 0.
+        */
+       if (!res)
+               res = 0x80000000;
+       return res;
+}
+
+
 static int inet6_netconf_dump_devconf(struct sk_buff *skb,
                                      struct netlink_callback *cb)
 {
@@ -739,8 +755,7 @@ static int inet6_netconf_dump_devconf(struct sk_buff *skb,
                idx = 0;
                head = &net->dev_index_head[h];
                rcu_read_lock();
-               cb->seq = atomic_read(&net->ipv6.dev_addr_genid) ^
-                         net->dev_base_seq;
+               cb->seq = inet6_base_seq(net);
                hlist_for_each_entry_rcu(dev, head, index_hlist) {
                        if (idx < s_idx)
                                goto cont;
@@ -5358,7 +5373,7 @@ static int inet6_dump_addr(struct sk_buff *skb, struct netlink_callback *cb,
        }
 
        rcu_read_lock();
-       cb->seq = atomic_read(&tgt_net->ipv6.dev_addr_genid) ^ tgt_net->dev_base_seq;
+       cb->seq = inet6_base_seq(tgt_net);
        for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
                idx = 0;
                head = &tgt_net->dev_index_head[h];