Patch "ipv4: properly combine dev_base_seq and ipv4.dev_addr_genid" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ipv4: properly combine dev_base_seq and ipv4.dev_addr_genid

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipv4-properly-combine-dev_base_seq-and-ipv4.dev_addr.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9b43784473250a3d5c495e11c9acae39667ef52a
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Thu Feb 15 17:21:06 2024 +0000

    ipv4: properly combine dev_base_seq and ipv4.dev_addr_genid
    
    [ 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@xxxxxxxxxx>
    Cc: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
    Acked-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index c511751c2f41a..425dfa8e4fd0a 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1797,6 +1797,21 @@ 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;
@@ -1848,8 +1863,7 @@ 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;
@@ -2250,8 +2264,7 @@ 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;