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

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Date:   Wed, 19 Jul 2017 11:23:05 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Ahern <dsahern@...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 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;