rtnetlink: Call nlmsg_parse() with correct header length

Signed-off-by: Michael Riesch <michael.riesch@omicron.at>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Benc <jbenc@redhat.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-kernel@vger.kernel.org
---
Habidere,

I encountered a netlink kernel warning when running avahi 0.6.31 on my system
with kernel v3.4.35 (it appears several times):

	netlink: 12 bytes leftover after parsing attributes.

Searching the web showed that commit "115c9b81928360d769a76c632bae62d15206a94a 
rtnetlink: Fix problem with buffer allocation" introduced this behaviour[1].

Now I - knowing nothing about netlink whatsoever - assume that the nlmsg_parse
function is called with the wrong header length. In user space the request
message consists out of the message header (struct nlmsghdr, 16 bytes) and an
ifinfomsg (struct ifinfomsg, 16 bytes). After that, request attributes could
follow. nlmsg_parse checks for this attributes after a given header length. In
rtnl_get_link() this header length is sizeof(struct ifinfomsg), but in
rtnl_calcit() as well as in rntl_dump_ifinfo() the header length is
sizeof(struct rtgenmsg), which is 1 byte.

With this patch I got rid of these warnings. However, I do not know whether
this is the correct solution, so I am looking forward to your comments.
Regards, Michael

[1] http://lists.infradead.org/pipermail/libnl/2012-April/000515.html

 net/core/rtnetlink.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

On Apr 8, 2013, at 8:45 AM, Michael Riesch <michael.riesch@omicron.at> wrote:

> 
> Signed-off-by: Michael Riesch <michael.riesch@omicron.at>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Benc <jbenc@redhat.com>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: linux-kernel@vger.kernel.org
> ---
> Habidere,
> 
> I encountered a netlink kernel warning when running avahi 0.6.31 on my system
> with kernel v3.4.35 (it appears several times):
> 
> 	netlink: 12 bytes leftover after parsing attributes.
> 
> Searching the web showed that commit "115c9b81928360d769a76c632bae62d15206a94a 
> rtnetlink: Fix problem with buffer allocation" introduced this behaviour[1].
> 
> Now I - knowing nothing about netlink whatsoever - assume that the nlmsg_parse
> function is called with the wrong header length. In user space the request
> message consists out of the message header (struct nlmsghdr, 16 bytes) and an
> ifinfomsg (struct ifinfomsg, 16 bytes). After that, request attributes could
> follow. nlmsg_parse checks for this attributes after a given header length. In
> rtnl_get_link() this header length is sizeof(struct ifinfomsg), but in
> rtnl_calcit() as well as in rntl_dump_ifinfo() the header length is
> sizeof(struct rtgenmsg), which is 1 byte.
> 
> With this patch I got rid of these warnings. However, I do not know whether
> this is the correct solution, so I am looking forward to your comments.
> Regards, Michael
> 
> [1] http://lists.infradead.org/pipermail/libnl/2012-April/000515.html
> 
> net/core/rtnetlink.c |    4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 900fc61..ebf6ace 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -1065,7 +1065,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
> 	rcu_read_lock();
> 	cb->seq = net->dev_base_seq;
> 
> -	if (nlmsg_parse(cb->nlh, sizeof(struct rtgenmsg), tb, IFLA_MAX,
> +	if (nlmsg_parse(cb->nlh, sizeof(struct ifinfomsg), tb, IFLA_MAX,
> 			ifla_policy) >= 0) {
> 
> 		if (tb[IFLA_EXT_MASK])
> @@ -1909,7 +1909,7 @@ static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
> 	u32 ext_filter_mask = 0;
> 	u16 min_ifinfo_dump_size = 0;
> 
> -	if (nlmsg_parse(nlh, sizeof(struct rtgenmsg), tb, IFLA_MAX,
> +	if (nlmsg_parse(nlh, sizeof(struct ifinfomsg), tb, IFLA_MAX,
> 			ifla_policy) >= 0) {
> 		if (tb[IFLA_EXT_MASK])
> 			ext_filter_mask = nla_get_u32(tb[IFLA_EXT_MASK]);
> -- 
> 1.7.9.5


I found that fcoemon has also been triggering these messages for some time. I found the same problem and arrived at exactly the same solution. I would have already sent it, but it is still in validation. As far as I am concerned:

Acked-by: Mark Rustad <mark.d.rustad@intel.com>

From: "Rustad, Mark D" <mark.d.rustad@intel.com>
Date: Mon, 8 Apr 2013 18:13:36 +0000

> On Apr 8, 2013, at 8:45 AM, Michael Riesch <michael.riesch@omicron.at> wrote:
> 
>> 
>> Signed-off-by: Michael Riesch <michael.riesch@omicron.at>
 ...
> I found that fcoemon has also been triggering these messages for
> some time. I found the same problem and arrived at exactly the same
> solution. I would have already sent it, but it is still in
> validation. As far as I am concerned:
> 
> Acked-by: Mark Rustad <mark.d.rustad@intel.com>

Looks good to me too, applied and queued up for -stable, thanks!
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