linux-kernel - [PATCH] netlink: fix append of whole original message on negative ack.

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Message-ID: <4900BFCF.2030707@gmail.com>
Date:	Thu, 23 Oct 2008 20:17:51 +0200
From:	M Lammertink <michellammertink@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] netlink: fix append of whole original message on negative
 ack.

From: Michel Lammertink <mlammertink <at> ti-wmc.nl>
Signed-off-by: Michel Lammertink <mlammertink <at> ti-wmc.nl>

Netlink can return an negative acknowledgement, which AFAICT should include an error code and the whole original message. This patch fixes the size argument given to the __nlmsg_put call. Without this patch only the original header was attached.
---

Can anyone explain to me why struct nlmsgerr contains an int error and the nlmsghdr struct. The comment in netlink_ack states that the whole message should be appended. Why not only include an int error in struct nlmsgerr and just append the original message?

Comments appreciated.

diff -uprN linux-2.6.27.3.orig/net/netlink/af_netlink.c linux-2.6.27.3/net/netlink/af_netlink.c
--- linux-2.6.27.3.orig/net/netlink/af_netlink.c	2008-10-23 18:01:54.000000000 +0200
+++ linux-2.6.27.3/net/netlink/af_netlink.c	2008-10-23 18:04:22.000000000 +0200
@@ -1656,7 +1656,7 @@ void netlink_ack(struct sk_buff *in_skb,
 	}

 	rep = __nlmsg_put(skb, NETLINK_CB(in_skb).pid, nlh->nlmsg_seq,
-			  NLMSG_ERROR, sizeof(struct nlmsgerr), 0);
+			  NLMSG_ERROR, payload, 0);
 	errmsg = nlmsg_data(rep);
 	errmsg->error = err;
 	memcpy(&errmsg->msg, nlh, err ? nlh->nlmsg_len : sizeof(*nlh));
--
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