linux-kernel - Re: [PATCH] rtnetlink: Call nlmsg_parse() with correct header length

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Date:	Mon, 8 Apr 2013 18:13:36 +0000
From:	"Rustad, Mark D" <mark.d.rustad@...el.com>
To:	Michael Riesch <michael.riesch@...cron.at>
CC:	"<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Benc <jbenc@...hat.com>, Theodore Ts'o <tytso@....edu>,
	"<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rtnetlink: Call nlmsg_parse() with correct header length

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

> 
> Signed-off-by: Michael Riesch <michael.riesch@...cron.at>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Benc <jbenc@...hat.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: linux-kernel@...r.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@...el.com>

-- 
Mark Rustad, Networking Division, Intel Corporation--
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