From f4479f3bc861a5f3865a537066080c1ec4949c39 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Tue, 5 Oct 2021 14:04:17 -0700
Subject: [PATCH] rtnetlink: fix if_nlmsg_stats_size() under estimation
Git-commit: d34367991933d28bd7331f67a759be9a8c474014
Patch-mainline: v5.15-rc5
References: stable-5.14.12

[ Upstream commit d34367991933d28bd7331f67a759be9a8c474014 ]

rtnl_fill_statsinfo() is filling skb with one mandatory if_stats_msg structure.

nlmsg_put(skb, pid, seq, type, sizeof(struct if_stats_msg), flags);

But if_nlmsg_stats_size() never considered the needed storage.

This bug did not show up because alloc_skb(X) allocates skb with
extra tailroom, because of added alignments. This could very well
be changed in the future to have deterministic behavior.

Fixes: 10c9ead9f3c6 ("rtnetlink: add new RTM_GETSTATS message to dump link stats")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Roopa Prabhu <roopa@nvidia.com>
Acked-by: Roopa Prabhu <roopa@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 net/core/rtnetlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 662eb1c37f47..10e2a0e4804b 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -5265,7 +5265,7 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 static size_t if_nlmsg_stats_size(const struct net_device *dev,
 				  u32 filter_mask)
 {
-	size_t size = 0;
+	size_t size = NLMSG_ALIGN(sizeof(struct if_stats_msg));
 
 	if (stats_attr_valid(filter_mask, IFLA_STATS_LINK_64, 0))
 		size += nla_total_size_64bit(sizeof(struct rtnl_link_stats64));
-- 
2.26.2