Re: [PATCH net-next] net: ethtool: fix NULL pointer dereference in pause_prepare_data()

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 24 Jan 2023 13:13:28 +0200 Vladimir Oltean wrote:
> In the following call path:
> 
> ethnl_default_dumpit
> -> ethnl_default_dump_one
>    -> ctx->ops->prepare_data
>       -> pause_prepare_data  
> 
> struct genl_info *info will be passed as NULL, and pause_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.
> 
> Fixes: 04692c9020b7 ("net: ethtool: netlink: retrieve stats from multiple sources (eMAC, pMAC)")
> Reported-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reported-by: syzbot+9d44aae2720fc40b8474@syzkaller.appspotmail.com