netdev - Re: [net PATCH] hsr: fix a NULL pointer dereference in hsr_dev

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Date:   Sat, 30 Nov 2019 10:35:58 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        treeze.taeung@...il.com
Subject: Re: [net PATCH] hsr: fix a NULL pointer dereference in hsr_dev_xmit()

On Sat, Nov 30, 2019 at 6:24 AM Taehee Yoo <ap420073@...il.com> wrote:
>
> hsr_dev_xmit() calls hsr_port_get_hsr() to find master node and that would
> return NULL if master node is not existing in the list.
> But hsr_dev_xmit() doesn't check return pointer so a NULL dereference
> could occur.

If you look at the git history, I made a same patch but reverted it later. :)


>
> In the TX datapath, there is no rcu_read_lock() so this patch adds missing
> rcu_read_lock() in the hsr_dev_xmit() too.

This is wrong.


>
> Test commands:
>     ip netns add nst
>     ip link add v0 type veth peer name v1
>     ip link add v2 type veth peer name v3
>     ip link set v1 netns nst
>     ip link set v3 netns nst
>     ip link add hsr0 type hsr slave1 v0 slave2 v2
>     ip a a 192.168.100.1/24 dev hsr0
>     ip link set v0 up
>     ip link set v2 up
>     ip link set hsr0 up
>     ip netns exec nst ip link add hsr1 type hsr slave1 v1 slave2 v3
>     ip netns exec nst ip a a 192.168.100.2/24 dev hsr1
>     ip netns exec nst ip link set v1 up
>     ip netns exec nst ip link set v3 up
>     ip netns exec nst ip link set hsr1 up
>     hping3 192.168.100.2 -2 --flood &
>     modprobe -rv hsr

Looks like the master port got deleted without respecting RCU
readers, let me look into it.

Thanks!