netdev - Re: [Patch net] net: check mac address length for dev_set_mac

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Date:   Thu, 20 Jul 2017 16:39:53 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:     David Ahern <dsahern@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net] net: check mac address length for dev_set_mac_address()

On Thu, Jul 20, 2017 at 11:27 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> dev_set_mac_address() accepts a struct sockaddr pointer as
> input but we have various types of mac addresse whose lengths
> are up to MAX_ADDR_LEN, this is confusing.
>
> Make it void like ->ndo_set_mac_address() and let callers check
> its length before calling it. It is too late to fix dev_ifsioc()
> due to API compatibility, so just reject those larger than
> sizeof(struct sockaddr).
>
> Fortunately, only a few IPv6 tunnel devices have addr_len
> larger than sizeof(struct sockaddr) and they don't support
> ndo_set_mac_addr(). But team driver seems still buggy without
> this patch.

Note, in team lb mode, I can successfully enslave ip6gre device
to a team device and make its mac addr look like:

# ip li show dev team0
17: team0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1448 qdisc noqueue
state UP mode DEFAULT group default qlen 1000
    link/gre6 00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00 brd
00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00

But ifconfig seems not recognize gre6 family, so it is just a matter of
a few lines of C code to trigger the bug.