Re: [PATCH 4.11] genetlink: fix counting regression on ctrl_dumpfamily()

[David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>]

From: Stanislaw Gruszka <sgruszka-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date: Wed, 22 Mar 2017 16:08:33 +0100

> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: Larry Finger <Larry.Finger-tQ5ms3gMjBLk1uMJSBkQmQ@public.gmane.org>
> Cc: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
> Fixes: 2ae0f17df1cd ("genetlink: use idr to track families")
> Signed-off-by: Stanislaw Gruszka <sgruszka-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

Applied and queued up for -stable, thanks.