linux-kernel - Re: [PATCH] net: rtnl: avoid uninitialized data in IFLA_VF_VLAN

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Date:   Fri, 30 Sep 2016 09:23:55 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Nogah Frankel <nogahf@...lanox.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: rtnl: avoid uninitialized data in IFLA_VF_VLAN_LIST handling

On Fri, Sep 30, 2016 at 9:13 AM, Arnd Bergmann <arnd@...db.de> wrote:
> With the newly added support for IFLA_VF_VLAN_LIST netlink messages,
> we get a warning about potential uninitialized variable use in
> the parsing of the user input when enabling the -Wmaybe-uninitialized
> warning:
>
> net/core/rtnetlink.c: In function 'do_setvfinfo':
> net/core/rtnetlink.c:1756:9: error: 'ivvl$' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> I have not been able to prove whether it is possible to arrive in
> this code with an empty IFLA_VF_VLAN_LIST block, but if we do,
> then ndo_set_vf_vlan gets called with uninitialized arguments.
>
> This adds an explicit check for an empty list, making it obvious
> to the reader and the compiler that this cannot happen.
>
> Fixes: 79aab093a0b5 ("net: Update API for VF vlan protocol 802.1ad support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  net/core/rtnetlink.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 3ac8946bf244..b06d2f46b83e 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -1753,6 +1753,9 @@ static int do_setvfinfo(struct net_device *dev, struct nlattr **tb)
>
>                         len++;
>                 }
> +               if (len == 0)
> +                       return -EINVAL;
> +
>                 err = ops->ndo_set_vf_vlan(dev, ivvl[0]->vf, ivvl[0]->vlan,
>                                            ivvl[0]->qos, ivvl[0]->vlan_proto);
>                 if (err < 0)
> --
> 2.9.0
>

So, if I read this code, we build an array, but call ndo_set_vf_vlan()
only using first element ?

Looks like the bug should be fixed in a different way.