[PATCH net v2] ethtool: fix ethtool msg len calculation for pause stats

ETHTOOL_A_PAUSE_STAT_MAX is the MAX attribute id,
so we need to subtract non-stats and add one to
get a count (IOW -2+1 == -1).

Otherwise we'll see:

  ethnl cmd 21: calculated reply length 40, but consumed 52

Fixes: 9a27a33027f2 ("ethtool: add standard pause stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v2: add a define

 include/linux/ethtool_netlink.h      | 3 +++
 include/uapi/linux/ethtool_netlink.h | 4 +++-
 net/ethtool/pause.c                  | 3 +--
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/ethtool_netlink.h b/include/linux/ethtool_netlink.h
index 1e7bf78cb382..aba348d58ff6 100644
--- a/include/linux/ethtool_netlink.h
+++ b/include/linux/ethtool_netlink.h

@@ -10,6 +10,9 @@
 #define __ETHTOOL_LINK_MODE_MASK_NWORDS \
 	DIV_ROUND_UP(__ETHTOOL_LINK_MODE_MASK_NBITS, 32)
 
+#define ETHTOOL_PAUSE_STAT_CNT	(__ETHTOOL_A_PAUSE_STAT_CNT -		\
+				 ETHTOOL_A_PAUSE_STAT_TX_FRAMES)
+
 enum ethtool_multicast_groups {
 	ETHNL_MCGRP_MONITOR,
 };

diff --git a/include/uapi/linux/ethtool_netlink.h b/include/uapi/linux/ethtool_netlink.h
index ca5fbb59fa42..999777d32dcf 100644
--- a/include/uapi/linux/ethtool_netlink.h
+++ b/include/uapi/linux/ethtool_netlink.h

@@ -411,7 +411,9 @@ enum {
 	ETHTOOL_A_PAUSE_STAT_TX_FRAMES,
 	ETHTOOL_A_PAUSE_STAT_RX_FRAMES,
 
-	/* add new constants above here */
+	/* add new constants above here
+	 * adjust ETHTOOL_PAUSE_STAT_CNT if adding non-stats!
+	 */
 	__ETHTOOL_A_PAUSE_STAT_CNT,
 	ETHTOOL_A_PAUSE_STAT_MAX = (__ETHTOOL_A_PAUSE_STAT_CNT - 1)
 };

diff --git a/net/ethtool/pause.c b/net/ethtool/pause.c
index 9009f412151e..ee1e5806bc93 100644
--- a/net/ethtool/pause.c
+++ b/net/ethtool/pause.c

@@ -56,8 +56,7 @@ static int pause_reply_size(const struct ethnl_req_info *req_base,
 
 	if (req_base->flags & ETHTOOL_FLAG_STATS)
 		n += nla_total_size(0) +	/* _PAUSE_STATS */
-			nla_total_size_64bit(sizeof(u64)) *
-				(ETHTOOL_A_PAUSE_STAT_MAX - 2);
+		     nla_total_size_64bit(sizeof(u64)) * ETHTOOL_PAUSE_STAT_CNT;
 	return n;
 }
 

-- 
2.31.1

On Tue, 2021-11-02 at 15:02 -0700, Jakub Kicinski wrote:

ETHTOOL_A_PAUSE_STAT_MAX is the MAX attribute id,
so we need to subtract non-stats and add one to
get a count (IOW -2+1 == -1).

Otherwise we'll see:

  ethnl cmd 21: calculated reply length 40, but consumed 52

Fixes: 9a27a33027f2 ("ethtool: add standard pause stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller [off-list ref]:

On Tue,  2 Nov 2021 15:02:36 -0700 you wrote:

ETHTOOL_A_PAUSE_STAT_MAX is the MAX attribute id,
so we need to subtract non-stats and add one to
get a count (IOW -2+1 == -1).

Otherwise we'll see:

  ethnl cmd 21: calculated reply length 40, but consumed 52

[...]

Here is the summary with links:
  - [net,v2] ethtool: fix ethtool msg len calculation for pause stats
    https://git.kernel.org/netdev/net/c/1aabe578dd86

You are awesome, thank you!
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