netdev - Re: [PATCH net-next] net: ethtool: fix NULL pointer dereference in stats_prepare

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Date:   Tue, 24 Jan 2023 16:23:47 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH net-next] net: ethtool: fix NULL pointer dereference in
 stats_prepare_data()

On Tue, 24 Jan 2023 13:08:01 +0200 Vladimir Oltean wrote:
> In the following call path:
> 
> ethnl_default_dumpit
> -> ethnl_default_dump_one
>    -> ctx->ops->prepare_data
>       -> stats_prepare_data  
> 
> struct genl_info *info will be passed as NULL, and stats_prepare_data()
> dereferences it while getting the extended ack pointer.
> 
> To avoid that, just set the extack to NULL if "info" is NULL, since the
> netlink extack handling messages know how to deal with that.
> 
> The pattern "info ? info->extack : NULL" is present in quite a few other
> "prepare_data" implementations, so it's clear that it's a more general
> problem to be dealt with at a higher level, but the code should have at
> least adhered to the current conventions to avoid the NULL dereference.

Choose one:
 - you disagree with my comment on the report
 - you don't think that we should mix the immediate fix with the
   structural change
 - you agree but "don't have the time" to fix this properly