[PATCH 2/3] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl_rx

[Fedor Pchelkin]

Currently, the synchronization between ath9k_wmi_cmd() and
ath9k_wmi_ctrl_rx() is exposed to races which can result, for example, not
only in wmi->cmd_rsp_buf being incorrectly initialized, but in overall
invalid behaviour of ath9k_wmi_cmd().

Consider the following scenario:

CPU0					CPU1

ath9k_wmi_cmd(...)
  mutex_lock(&wmi->op_mutex)
  ath9k_wmi_cmd_issue(...)
  wait_for_completion_timeout(...)
  ---
  timeout
  ---
  mutex_unlock(&wmi->op_mutex)
  return -ETIMEDOUT

ath9k_wmi_cmd(...)
  mutex_lock(&wmi->op_mutex)
  ath9k_wmi_cmd_issue(...)
  wait_for_completion_timeout(...)
					/* the one left after the first
					 * ath9k_wmi_cmd call
					 */
					ath9k_wmi_rsp_callback(...)
					  memcpy(...)
					  complete(&wmi->cmd_wait);
  /* Awakened by the bogus callback
   * => invalid return
   */
  mutex_unlock(&wmi->op_mutex)
  return 0

This may occur even on uniprocessor machines, and in SMP case the races
may be even more intricate.

To fix this, move the contents of ath9k_wmi_rsp_callback() under wmi_lock
inside ath9k_wmi_ctrl_rx() so that the wmi->cmd_wait can be completed only
for initially designated wmi_cmd call, otherwise the path would be
rejected with last_seq_id check.

Also move recording the rsp buffer and length into ath9k_wmi_cmd_issue()
under the same wmi_lock with last_seq_id update to avoid their racy
changes.

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

Fixes: fb9987d0f748 ("ath9k_htc: Support for AR9271 chipset.")
Reported-and-tested-by: syzbot+df61b36319e045c00a08@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
---
This patch depends on [PATCH 1/3] wifi: ath9k: avoid referencing uninit
memory in ath9k_wmi_ctrl_rx

 drivers/net/wireless/ath/ath9k/wmi.c | 48 ++++++++++++++--------------
 1 file changed, 24 insertions(+), 24 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
index 2e7c361b62f5..99a91bbaace9 100644
--- a/drivers/net/wireless/ath/ath9k/wmi.c
+++ b/drivers/net/wireless/ath/ath9k/wmi.c
@@ -200,20 +200,6 @@ void ath9k_fatal_work(struct work_struct *work)
 	ath9k_htc_reset(priv);
 }
 
-static void ath9k_wmi_rsp_callback(struct wmi *wmi, struct sk_buff *skb)
-{
-	skb_pull(skb, sizeof(struct wmi_cmd_hdr));
-
-	/* Once again validate the SKB. */
-	if (unlikely(skb->len < wmi->cmd_rsp_len))
-		return;
-
-	if (wmi->cmd_rsp_buf != NULL && wmi->cmd_rsp_len != 0)
-		memcpy(wmi->cmd_rsp_buf, skb->data, wmi->cmd_rsp_len);
-
-	complete(&wmi->cmd_wait);
-}
-
 static void ath9k_wmi_ctrl_rx(void *priv, struct sk_buff *skb,
 			      enum htc_endpoint_id epid)
 {
@@ -242,14 +228,26 @@ static void ath9k_wmi_ctrl_rx(void *priv, struct sk_buff *skb,
 
 	/* Check if there has been a timeout. */
 	spin_lock_irqsave(&wmi->wmi_lock, flags);
-	if (be16_to_cpu(hdr->seq_no) != wmi->last_seq_id) {
+	if (be16_to_cpu(hdr->seq_no) != wmi->last_seq_id ||
+	    be16_to_cpu(hdr->seq_no) == 0) {
+		spin_unlock_irqrestore(&wmi->wmi_lock, flags);
+		goto free_skb;
+	}
+
+	/* Next, process WMI command response */
+	skb_pull(skb, sizeof(struct wmi_cmd_hdr));
+
+	/* Once again validate the SKB. */
+	if (unlikely(skb->len < wmi->cmd_rsp_len)) {
 		spin_unlock_irqrestore(&wmi->wmi_lock, flags);
 		goto free_skb;
 	}
-	spin_unlock_irqrestore(&wmi->wmi_lock, flags);
 
-	/* WMI command response */
-	ath9k_wmi_rsp_callback(wmi, skb);
+	if (wmi->cmd_rsp_buf != NULL && wmi->cmd_rsp_len != 0)
+		memcpy(wmi->cmd_rsp_buf, skb->data, wmi->cmd_rsp_len);
+
+	complete(&wmi->cmd_wait);
+	spin_unlock_irqrestore(&wmi->wmi_lock, flags);
 
 free_skb:
 	kfree_skb(skb);
@@ -287,7 +285,8 @@ int ath9k_wmi_connect(struct htc_target *htc, struct wmi *wmi,
 
 static int ath9k_wmi_cmd_issue(struct wmi *wmi,
 			       struct sk_buff *skb,
-			       enum wmi_cmd_id cmd, u16 len)
+			       enum wmi_cmd_id cmd, u16 len,
+			       u8 *rsp_buf, u32 rsp_len)
 {
 	struct wmi_cmd_hdr *hdr;
 	unsigned long flags;
@@ -297,6 +296,11 @@ static int ath9k_wmi_cmd_issue(struct wmi *wmi,
 	hdr->seq_no = cpu_to_be16(++wmi->tx_seq_id);
 
 	spin_lock_irqsave(&wmi->wmi_lock, flags);
+
+	/* record the rsp buffer and length */
+	wmi->cmd_rsp_buf = rsp_buf;
+	wmi->cmd_rsp_len = rsp_len;
+
 	wmi->last_seq_id = wmi->tx_seq_id;
 	spin_unlock_irqrestore(&wmi->wmi_lock, flags);
 
@@ -337,11 +341,7 @@ int ath9k_wmi_cmd(struct wmi *wmi, enum wmi_cmd_id cmd_id,
 		goto out;
 	}
 
-	/* record the rsp buffer and length */
-	wmi->cmd_rsp_buf = rsp_buf;
-	wmi->cmd_rsp_len = rsp_len;
-
-	ret = ath9k_wmi_cmd_issue(wmi, skb, cmd_id, cmd_len);
+	ret = ath9k_wmi_cmd_issue(wmi, skb, cmd_id, cmd_len, rsp_buf, rsp_len);
 	if (ret)
 		goto out;
 
-- 
2.34.1