From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next] scm: Don't use struct ucred in NETLINK_CB and
 struct scm_cookie.
Date: Fri, 07 Sep 2012 17:07:26 +0200
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Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org,
	"Serge E. Hallyn" <serge@hallyn.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
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On Thu, 2012-09-06 at 21:20 -0700, Eric W. Biederman wrote:
> Passing uids and gids on NETLINK_CB from a process in one user
> namespace to a process in another user namespace can result in the
> wrong uid or gid being presented to userspace.  Avoid that problem by
> passing kuids and kgids instead.
> 
> - define struct scm_creds for use in scm_cookie and netlink_skb_parms
>   that holds uid and gid information in kuid_t and kgid_t.
> 
> - Modify scm_set_cred to fill out scm_creds by heand instead of using
>   cred_to_ucred to fill out struct ucred.  This conversion ensures
>   userspace does not get incorrect uid or gid values to look at.
> 
> - Modify scm_recv to convert from struct scm_creds to struct ucred
>   before copying credential values to userspace.
> 
> - Modify __scm_send to populate struct scm_creds on in the scm_cookie,
>   instead of just copying struct ucred from userspace.
> 
> - Modify netlink_sendmsg to copy scm_creds instead of struct ucred
>   into the NETLINK_CB.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>


> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 7cb7867..6473267 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -1398,7 +1398,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
>  
>  	NETLINK_CB(skb).pid	= nlk->pid;
>  	NETLINK_CB(skb).dst_group = dst_group;
> -	memcpy(NETLINK_CREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
> +	NETLINK_CB(skb).creds	= siocb->scm->creds;
>  
>  	err = -EFAULT;
>  	if (memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len)) {

Seems fine to me, but I am not sure why you kept NETLINK_CREDS()
defined/used once.