[PATCH net] rtnetlink: fix if_nlmsg_stats_size() under estimation

From: Eric Dumazet <edumazet@google.com>

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 <redacted>
---
 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 972c8cb303a514758278307cd9fcb974e37f2b96..8ccce85562a1da2a5285aebd19a6a4cb7d6a163e 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c

@@ -5262,7 +5262,7 @@ 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));

-- 
2.33.0.800.g4c38ced690-goog

On 10/5/21 2:04 PM, Eric Dumazet wrote:

From: Eric Dumazet <edumazet@google.com>

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 <redacted>
---

Acked-by: Roopa Prabhu <redacted>

don't know how i missed this. Thanks for the patch Eric.

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue,  5 Oct 2021 14:04:17 -0700 you wrote:

From: Eric Dumazet <edumazet@google.com>

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.

[...]

Here is the summary with links:
  - [net] rtnetlink: fix if_nlmsg_stats_size() under estimation
    https://git.kernel.org/netdev/net/c/d34367991933

You are awesome, thank you!
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