linux-kernel - Re: [PATCH net] nfp: bpf: prevent integer overflow in nfp_bpf_event

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Message-ID: <ae4d008f-8a70-4c0d-a5c8-c480cad53cf5@intel.com>
Date: Tue, 14 Jan 2025 18:17:22 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
CC: Jakub Kicinski <kuba@...nel.org>, Louis Peens <louis.peens@...igine.com>,
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, "Quentin
 Monnet" <qmo@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
	<bpf@...r.kernel.org>, <oss-drivers@...igine.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH net] nfp: bpf: prevent integer overflow in
 nfp_bpf_event_output()

From: Dan Carpenter <dan.carpenter@...aro.org>
Date: Tue, 14 Jan 2025 13:45:04 +0300

> [ I tried to send this email yesterday but apparently gmail blocked
>   it for security reasons?  So weird. - dan ]
> 
> On Mon, Jan 13, 2025 at 01:32:11PM +0100, Alexander Lobakin wrote:
>> From: Dan Carpenter <dan.carpenter@...aro.org>
>> Date: Mon, 13 Jan 2025 09:18:39 +0300
>>
>>> The "sizeof(struct cmsg_bpf_event) + pkt_size + data_size" math could
>>> potentially have an integer wrapping bug on 32bit systems.  Check for
>>
>> Not in practice I suppose? Do we need to fix "never" bugs?
>>
> 
> No, this is from static analysis.  We don't need to fix never bugs.
> 
> This is called from nfp_bpf_ctrl_msg_rx() and nfp_bpf_ctrl_msg_rx_raw()
> and I assumed that since pkt_size and data_size come from skb->data on
> the rx path then they couldn't be trusted.

skbs are always valid and skb->len could never cross INT_MAX to provoke
an overflow.

> 
> Where is the bounds checking?
> 
> regards,
> dan carpenter

Thanks,
Olek