netdev - Re: [PATCH net] net: nexthop: Initialize all fields in dumped nexthops

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Message-ID: <CANn89iJQB4Po=J32rg10CNE+hrGqGZWfdWqKPdY6FK0UgQpxXg@mail.gmail.com>
Date: Tue, 23 Jul 2024 18:50:24 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Petr Machata <petrm@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	David Ahern <dsahern@...nel.org>, mlxsw@...dia.com, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net] net: nexthop: Initialize all fields in dumped nexthops

On Tue, Jul 23, 2024 at 6:05 PM Petr Machata <petrm@...dia.com> wrote:
>
> struct nexthop_grp contains two reserved fields that are not initialized by
> nla_put_nh_group(), and carry garbage. This can be observed e.g. with
> strace (edited for clarity):
>
>     # ip nexthop add id 1 dev lo
>     # ip nexthop add id 101 group 1
>     # strace -e recvmsg ip nexthop get id 101
>     ...
>     recvmsg(... [{nla_len=12, nla_type=NHA_GROUP},
>                  [{id=1, weight=0, resvd1=0x69, resvd2=0x67}]] ...) = 52
>
> The fields are reserved and therefore not currently used. But as they are, they
> leak kernel memory, and the fact they are not just zero complicates repurposing
> of the fields for new ends. Initialize the full structure.
>
> Fixes: 430a049190de ("nexthop: Add support for nexthop groups")
> Signed-off-by: Petr Machata <petrm@...dia.com>
> Reviewed-by: Ido Schimmel <idosch@...dia.com>

Interesting... not sure why syzbot did not catch this one.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>