[PATCH v2] wifi: ath9k: avoid referencing uninit memory in ath9k_wmi_ctrl_rx

[Fedor Pchelkin]

For the reasons also described in commit b383e8abed41 ("wifi: ath9k: avoid
uninit memory read in ath9k_htc_rx_msg()"), ath9k_htc_rx_msg() should
validate pkt_len before accessing the SKB.

For example, the obtained SKB may have been badly constructed with
pkt_len = 8. In this case, the SKB can only contain a valid htc_frame_hdr
but after being processed in ath9k_htc_rx_msg() and passed to
ath9k_wmi_ctrl_rx() endpoint RX handler, it is expected to have a WMI
command header which should be located inside its data payload. 

Implement sanity checking inside ath9k_wmi_ctrl_rx(). Otherwise, uninit
memory can be referenced.

Tested on Qualcomm Atheros Communications AR9271 802.11n .

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: fb9987d0f748 ("ath9k_htc: Support for AR9271 chipset.")
Reported-and-tested-by: syzbot+f2cb6e0ffdb961921e4d@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
---
v2: remove incorrect checks and rephrase commit info

 drivers/net/wireless/ath/ath9k/wmi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
index 19345b8f7bfd..d652c647d56b 100644
--- a/drivers/net/wireless/ath/ath9k/wmi.c
+++ b/drivers/net/wireless/ath/ath9k/wmi.c
@@ -221,6 +221,10 @@ static void ath9k_wmi_ctrl_rx(void *priv, struct sk_buff *skb,
 	if (unlikely(wmi->stopped))
 		goto free_skb;
 
+	/* Validate the obtained SKB. */
+	if (unlikely(skb->len < sizeof(struct wmi_cmd_hdr)))
+		goto free_skb;
+
 	hdr = (struct wmi_cmd_hdr *) skb->data;
 	cmd_id = be16_to_cpu(hdr->command_id);
 
-- 
2.34.1