netdev - Re: [PATCH net] rtnetlink: Fix handling of disabled L3 stats in RTM

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Date:   Wed, 13 Apr 2022 09:10:39 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Petr Machata <petrm@...dia.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net] rtnetlink: Fix handling of disabled L3 stats in
 RTM_GETSTATS replies

On Tue, Apr 12, 2022 at 10:25:06PM +0200, Petr Machata wrote:
> When L3 stats are disabled, rtnl_offload_xstats_get_size_stats() returns
> size of 0, which is supposed to be an indication that the corresponding
> attribute should not be emitted. However, instead, the current code
> reserves a 0-byte attribute.
> 
> The reason this does not show up as a citation on a kasan kernel is that
> netdev_offload_xstats_get(), which is supposed to fill in the data, never
> ends up getting called, because rtnl_offload_xstats_get_stats() notices
> that the stats are not actually used and skips the call.
> 
> Thus a zero-length IFLA_OFFLOAD_XSTATS_L3_STATS attribute ends up in a
> response, confusing the userspace.
> 
> Fix by skipping the L3-stats related block in rtnl_offload_xstats_fill().
> 
> Fixes: 0e7788fd7622 ("net: rtnetlink: Add UAPI for obtaining L3 offload xstats")
> Signed-off-by: Petr Machata <petrm@...dia.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>