linux-hardening - Re: [Patch net-next resend v2] net: use %px to print skb address in trace_netif_receive

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Date:   Fri, 23 Jul 2021 00:09:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Qitao Xu <qitao.xu@...edance.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [Patch net-next resend v2] net: use %px to print skb address in
 trace_netif_receive_skb

On Wed, Jul 14, 2021 at 10:59:23PM -0700, Cong Wang wrote:
> From: Qitao Xu <qitao.xu@...edance.com>
> 
> The print format of skb adress in tracepoint class net_dev_template
> is changed to %px from %p, because we want to use skb address
> as a quick way to identify a packet.

No; %p was already hashed to uniquely identify unique addresses. This
is needlessly exposing kernel addresses with no change in utility. See
[1] for full details on when %px is justified (almost never).

> Note, trace ring buffer is only accessible to privileged users,
> it is safe to use a real kernel address here.

That's not accurate either; there is a difference between uid 0 and
kernel mode privilege levels.

Please revert these:

	851f36e40962408309ad2665bf0056c19a97881c
	65875073eddd24d7b3968c1501ef29277398dc7b

And adjust this to replace %px with %p:

	70713dddf3d25a02d1952f8c5d2688c986d2f2fb

Thanks!

-Kees

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#p-format-specifier

> 
> Reviewed-by: Cong Wang <cong.wang@...edance.com>
> Signed-off-by: Qitao Xu <qitao.xu@...edance.com>
> ---
>  include/trace/events/net.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/net.h b/include/trace/events/net.h
> index 2399073c3afc..78c448c6ab4c 100644
> --- a/include/trace/events/net.h
> +++ b/include/trace/events/net.h
> @@ -136,7 +136,7 @@ DECLARE_EVENT_CLASS(net_dev_template,
>  		__assign_str(name, skb->dev->name);
>  	),
>  
> -	TP_printk("dev=%s skbaddr=%p len=%u",
> +	TP_printk("dev=%s skbaddr=%px len=%u",
>  		__get_str(name), __entry->skbaddr, __entry->len)
>  )
>  
> -- 
> 2.27.0
> 

-- 
Kees Cook