[PATCH 6.6 245/299] ipv4: properly combine dev_base_seq and ipv4.dev_addr_genid

Greg Kroah-Hartman
2024-02-27T13:59:07Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 081a0e3b0d4c061419d3f4679dec9f68725b17e4 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/devinet.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index ca0ff15dc8fa3..bc74f131fe4df 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1825,6 +1825,21 @@ static int in_dev_dump_addr(struct in_device *in_dev, struct sk_buff *skb,
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;
--
2.43.0