netdev - Re: out-of-bounds access with virtio-net

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Date:   Wed, 19 Jul 2017 12:33:34 -0600
From:   David Ahern <dsahern@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: out-of-bounds access with virtio-net

On 7/19/17 12:23 PM, Cong Wang wrote:
> On Wed, Jul 19, 2017 at 9:59 AM, David Ahern <dsahern@...il.com> wrote:
>> Changing the mac address on a virtio-net based nic is triggering an
>> out-of-bounds access. Nothing fancy with the command:
>>
>> ip li set dev eth2 addr 01:02:34:56:78:9a
>>
>> virtnet_set_mac_address is calling kmemdup for sizeof sockaddr, yet only
>> ETH_ALEN + sizeof(sa_family_t) bytes were malloc'ed.
> 
> Previously we have a dev->addr_len longer than sizeof sockaddr,
> now we a shorter one... This mac addr thing is really a mess currently.
> 
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index d1ba90980be1..d13bebdf6465 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -2031,7 +2031,7 @@ static int do_setlink(const struct sk_buff *skb,
>                 struct sockaddr *sa;
>                 int len;
> 
> -               len = sizeof(sa_family_t) + dev->addr_len;
> +               len = sizeof(sa_family_t) + max(dev->addr_len, sizeof(*sa));
>                 sa = kmalloc(len, GFP_KERNEL);
>                 if (!sa) {
>                         err = -ENOMEM;
> 

seems reasonable. I am heading to the mountains in a few hours; won't
have time to test until Friday. Please submit formally; no need to wait
for me.