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

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

[M Lammertink]

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));

Re: [PATCH] netlink: fix append of whole original message on negative ack.

[David Miller]

From: M Lammertink <michellammertink@gmail.com>
Date: Thu, 23 Oct 2008 20:17:51 +0200

You'll get a much better review of this if you send it to
the netdev mailing list, which is where all the networking
developers are subscribed.  They don't read linux-kernel

Added to CC:

> 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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Re: [PATCH] netlink: fix append of whole original message on negative ack.

[Evgeniy Polyakov]

Hi.

On Thu, Oct 23, 2008 at 01:45:13PM -0700, David Miller (davem@davemloft.net) wrote:
> > 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?

Having header (even seq/pid only) is enough to find a message
for that userspace which cares. Looks like your patch can break
existing applications which are used to work with header only,
even if that was a mistake? Although application is supposed to
check the length, it still can expect only a header. I have to
note, that I do not know any such application though.

-- 
	Evgeniy Polyakov

Re: [PATCH] netlink: fix append of whole original message on negative ack.

[Patrick McHardy]

David Miller wrote:
> From: M Lammertink <michellammertink@gmail.com>
> Date: Thu, 23 Oct 2008 20:17:51 +0200
>   
>> 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)

You can't include the full message since the resulting message
might exceed the 64k netlink limit.