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

Message ID 20210502212611.1818-1-phil@philpotter.co.uk
State New
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  • [v2] ath9k: ath9k_htc_rx_msg: return when sk_buff is too small
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Commit Message

Phillip Potter May 2, 2021, 9:26 p.m.
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: syzbot+e4534e8c1c382508312c@syzkaller.appspotmail.com
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
---

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(+)

Comments

Kalle Valo May 30, 2021, 9 a.m. | #1
Phillip Potter <phil@philpotter.co.uk> 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: syzbot+e4534e8c1c382508312c@syzkaller.appspotmail.com

> Signed-off-by: Phillip Potter <phil@philpotter.co.uk>

> ---

>

> 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;
	}

-- 
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

Patch

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;
+	}
+
 	htc_hdr = (struct htc_frame_hdr *) skb->data;
 	epid = htc_hdr->endpoint_id;