[PATCH 5.10 106/122] ipv6: properly combine dev_base_seq and ipv6.dev_addr_genid

Greg Kroah-Hartman
2024-02-27T14:31:21Z

From: Eric Dumazet <edumazet@google.com>

[ 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>
---
net/ipv6/addrconf.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 79787a1f5ab34..150c2f71ec89f 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -698,6 +698,22 @@ static int inet6_netconf_get_devconf(struct sk_buff *in_skb,
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)
{
@@ -731,8 +747,7 @@ 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;
@@ -5288,7 +5303,7 @@ 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];
--
2.43.0