ipv4: properly combine dev_base_seq and ipv4.dev_addr_genid

net->dev_base_seq and ipv4.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: 0465277f6b3f ("ipv4: provide addr and netconf dump consistency info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index ca0ff15dc8fa358b81a804eda7398ecd10f00743..bc74f131fe4dfad327e71c1a8f0a4b66cdc526e5 100644 (file)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1825,6 +1825,21 @@ done:
        return err;
 }
 
+/* Combine dev_addr_genid and dev_base_seq to detect changes.
+ */
+static u32 inet_base_seq(const struct net *net)
+{
+       u32 res = atomic_read(&net->ipv4.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 inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 {
        const struct nlmsghdr *nlh = cb->nlh;
@@ -1876,8 +1891,7 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
                idx = 0;
                head = &tgt_net->dev_index_head[h];
                rcu_read_lock();
-               cb->seq = atomic_read(&tgt_net->ipv4.dev_addr_genid) ^
-                         tgt_net->dev_base_seq;
+               cb->seq = inet_base_seq(tgt_net);
                hlist_for_each_entry_rcu(dev, head, index_hlist) {
                        if (idx < s_idx)
                                goto cont;
@@ -2278,8 +2292,7 @@ static int inet_netconf_dump_devconf(struct sk_buff *skb,
                idx = 0;
                head = &net->dev_index_head[h];
                rcu_read_lock();
-               cb->seq = atomic_read(&net->ipv4.dev_addr_genid) ^
-                         net->dev_base_seq;
+               cb->seq = inet_base_seq(net);
                hlist_for_each_entry_rcu(dev, head, index_hlist) {
                        if (idx < s_idx)
                                goto cont;