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Date:   Thu, 23 Mar 2017 11:45:17 +0100
From:   poma <pomidorabelisima@...il.com>
To:     Stanislaw Gruszka <sgruszka@...hat.com>, netdev@...r.kernel.org
Cc:     linux-wireless@...r.kernel.org,
        Xose Vazquez Perez <xose.vazquez@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH 4.11] genetlink: fix counting regression on
 ctrl_dumpfamily()

On 22.03.2017 16:08, Stanislaw Gruszka wrote:
> Commit 2ae0f17df1cd ("genetlink: use idr to track families") replaced
> 
> 	if (++n < fams_to_skip)
> 		continue;
> into:
> 
> 	if (n++ < fams_to_skip)
> 		continue;
> 
> This subtle change cause that on retry ctrl_dumpfamily() call we omit
> one family that failed to do ctrl_fill_info() on previous call, because
> cb->args[0] = n number counts also family that failed to do
> ctrl_fill_info().
> 
> Patch fixes the problem and avoid confusion in the future just decrease
> n counter when ctrl_fill_info() fail.
> 
> User visible problem caused by this bug is failure to get access to
> some genetlink family i.e. nl80211. However problem is reproducible
> only if number of registered genetlink families is big enough to
> cause second call of ctrl_dumpfamily().
> 
> Cc: Xose Vazquez Perez <xose.vazquez@...il.com>
> Cc: Larry Finger <Larry.Finger@...inger.net>
> Cc: Johannes Berg <johannes@...solutions.net>
> Fixes: 2ae0f17df1cd ("genetlink: use idr to track families")
> Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
> ---
> Dave, please also target this for 4.10+ -stable.
> 
>  net/netlink/genetlink.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
> index fb6e10f..92e0981 100644
> --- a/net/netlink/genetlink.c
> +++ b/net/netlink/genetlink.c
> @@ -783,8 +783,10 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb)
>  
>  		if (ctrl_fill_info(rt, NETLINK_CB(cb->skb).portid,
>  				   cb->nlh->nlmsg_seq, NLM_F_MULTI,
> -				   skb, CTRL_CMD_NEWFAMILY) < 0)
> +				   skb, CTRL_CMD_NEWFAMILY) < 0) {
> +			n--;
>  			break;
> +		}
>  	}
>  
>  	cb->args[0] = n;
> 


Thanks Stanislaw, Larry!

Tested-by: poma <poma@...il.com>

Ref.
https://bugzilla.redhat.com/show_bug.cgi?id=1422247

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