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

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Message-ID: <CAM_iQpXG-3XBxKxPR5s8jyZEZthaBaG73No3DOqr78aWNn1c3w@mail.gmail.com>
Date:   Wed, 4 Dec 2019 09:29:56 -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.
>
> In the TX datapath, there is no rcu_read_lock() so this patch adds missing
> rcu_read_lock() in the hsr_dev_xmit() too.

Just a correction:
The TX path _has_ RCU read lock, but it harms nothing to take it again.

[...]
>
> Fixes: 311633b60406 ("hsr: switch ->dellink() to ->ndo_uninit()")
> Signed-off-by: Taehee Yoo <ap420073@...il.com>

This fix is correct. There is no other way to workaround this RCU
rule, checking against NULL is the only way to fix RCU reader
races, so:

Acked-by: Cong Wang <xiyou.wangcong@...il.com>


Taehee, you might have to resend this with my Acked-by as David
probably already drops it from patchwork.

Thanks.