Subject: Re: [PATCH v2] ath9k: ath9k_htc_rx_msg: return when sk_buff is too small

From: Kalle Valo <[email-masked]>
Date: Sun, 30 May 2021 12:00:53 +0300

Phillip Potter <[email-masked]> writes:

> At the start of ath9k_htc_rx_msg, we check to see if the skb pointer is
> valid, but what we don't do is check if it is large enough to contain a
> valid struct htc_frame_hdr. We should check for this and return if not,
> as the buffer is invalid in this case. Fixes a KMSAN-found uninit-value bug
> reported by syzbot at:
> https://syzkaller.appspot.com/bug?id=7dccb7d9ad4251df1c49f370607a49e1f09644ee
>
> Reported-by: [email-masked]
> Signed-off-by: Phillip Potter <[email-masked]>
> ---
>
> V2:
> * Free skb properly when this problem is detected, as pointed out by
>   Florian Westphal.
>
> ---
>  drivers/net/wireless/ath/ath9k/htc_hst.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ath9k/htc_hst.c b/drivers/net/wireless/ath/ath9k/htc_hst.c
> index 510e61e97dbc..1fe89b068ac4 100644
> --- a/drivers/net/wireless/ath/ath9k/htc_hst.c
> +++ b/drivers/net/wireless/ath/ath9k/htc_hst.c
> @@ -406,6 +406,11 @@ void ath9k_htc_rx_msg(struct htc_target *htc_handle,
>  	if (!htc_handle || !skb)
>  		return;
>  
> +	if (!pskb_may_pull(skb, sizeof(struct htc_frame_hdr))) {
> +		kfree_skb(skb);
> +		return;
> +	}

This does not look complete to me, I think the function is missing
proper length checks. For example, with ENDPOINT0 it reads two byte
msg_id after the htc header and it's not verified that skb really has
that. I did not check if ep_callbacks.rx handlers have proper length
handling, I recommend verifying that also while fixing this.

Also I want to point out that the skb is freed differently based on
endpoint, I did not check why and don't know if it causes:

	if (epid < 0 || epid >= ENDPOINT_MAX) {
		if (pipe_id != USB_REG_IN_PIPE)
			dev_kfree_skb_any(skb);
		else
			kfree_skb(skb);
		return;
	}

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