netdev - Re: [PATCH] Do not listen if rtnl_send() fails in ip link iplink_have

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Date:	Wed, 11 Dec 2013 10:57:49 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Petr Písař <ppisar@...hat.com>
Cc:	<netdev@...r.kernel.org>
Subject: Re: [PATCH] Do not listen if rtnl_send() fails in ip link
 iplink_have_newlink() test

On Wed, 11 Dec 2013 14:01:29 +0100
Petr Písař <ppisar@...hat.com> wrote:

> If rtnl_send() fails in iplink_have_newlink() test, listening for
> response will result in indefinite hang. This can be demonstrated by
> "ip link show" while SELinux preventing from sending the RTM_NEWLINK
> over netlink.
> 
> This patch checks for the return value as is done at all other
> rtnl_send() calls.
> 
> Signed-off-by: Petr Písař <ppisar@...hat.com>
> ---
>  ip/iplink.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/ip/iplink.c b/ip/iplink.c
> index 58b6c20..f7d9e17 100644
> --- a/ip/iplink.c
> +++ b/ip/iplink.c
> @@ -178,8 +178,8 @@ static int iplink_have_newlink(void)
>  		req.n.nlmsg_type = RTM_NEWLINK;
>  		req.i.ifi_family = AF_UNSPEC;
>  
> -		rtnl_send(&rth, &req.n, req.n.nlmsg_len);
> -		rtnl_listen(&rth, accept_msg, NULL);
> +		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) >= 0)
> +			rtnl_listen(&rth, accept_msg, NULL);
>  	}
>  	return have_rtnl_newlink;
>  }

I think it should print an error messag, not silently ignore the send failure.
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