netdev - Re: [PATCH 1/4] nfc: Extract nfc_dev access from nfc_alloc_send

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Date: Mon, 27 Nov 2023 11:10:51 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Siddh Raman Pant <code@...dh.me>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] nfc: Extract nfc_dev access from nfc_alloc_send_skb()
 into the callers

On 25/11/2023 21:26, Siddh Raman Pant wrote:
> The only reason why nfc_dev was accessed inside nfc_alloc_send_skb() is
> for getting the headroom and tailroom values.
> 
> This can cause UAF to be reported from nfc_alloc_send_skb(), but the
> callers are responsible for managing the device access, and thus the
> UAF being reported, as the callers (like nfc_llcp_send_ui_frame()) may
> repeatedly call this function, and this function will repeatedly try
> to get the same headroom and tailroom values.

I don't understand this sentence.

"This can cause ..., but ...". But starts another clause which should be
in contradictory to previous one.

> 
> Thus, put the nfc_dev access responsibility on the callers and accept
> the headroom and tailroom values directly.

Is this a fix or improvement? If fix, is the UAF real? If so, you miss
Fixes tag.

Best regards,
Krzysztof