linux-kernel - Re: [PATCH] net: usbnet: Fix potential NULL pointer dereference

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Date:   Mon, 6 Nov 2023 13:59:08 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Ren Mingshuai <renmingshuai@...wei.com>, kuba@...nel.org,
        Bjørn Mork <bjorn@...k.no>
Cc:     caowangbao@...wei.com, davem@...emloft.net, khlebnikov@...nvz.org,
        liaichun@...wei.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, oneukum@...e.com, yanan@...wei.com
Subject: Re: [PATCH] net: usbnet: Fix potential NULL pointer dereference

On 02.11.23 10:06, Ren Mingshuai wrote:

>> What do you mean? Grepping the function name shows call sites with NULL getting passed as skb.

You may see that we do check skb != NULL before we timestamp it.
But later in the process we depend skb == NULL implying that tx_fixup != NULL

That is the combination that must not happen. If it happens, though
simply bailing out seems to the wrong answer.
  
> Yes And I just learned that during the cdc_ncm_driver.probe, it is possible to pass a NULL SKB to usbnet_start_xmit().

How can that happen? And if it happens is tx_fixup set?

	Regards
		Oliver