[PATCH v2] wifi: ath9k: fix races between ath9k_wmi_cmd and ath9k_wmi_ctrl_rx

Fedor Pchelkin
2023-04-24T19:19:28Z

Currently, the synchronization between ath9k_wmi_cmd() and
ath9k_wmi_ctrl_rx() is exposed to a race condition which, although being
rather unlikely, can lead to 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
---
/* the callback is being processed
* before last_seq_id became zero
*/
ath9k_wmi_ctrl_rx(...)
spin_lock_irqsave(...)
/* wmi->last_seq_id check here
* doesn't detect timeout yet
*/
spin_unlock_irqrestore(...)
/* last_seq_id is zeroed to
* indicate there was a timeout
*/
wmi->last_seq_id = 0
mutex_unlock(&wmi->op_mutex)
return -ETIMEDOUT

ath9k_wmi_cmd(...)
mutex_lock(&wmi->op_mutex)
/* the buffer is replaced with
* another one
*/
wmi->cmd_rsp_buf = rsp_buf
wmi->cmd_rsp_len = rsp_len
ath9k_wmi_cmd_issue(...)
spin_lock_irqsave(...)
spin_unlock_irqrestore(...)
wait_for_completion_timeout(...)
/* the continuation of the
* callback left after the first
* ath9k_wmi_cmd call
*/
ath9k_wmi_rsp_callback(...)
/* copying data designated
* to already timeouted
* WMI command into an
* inappropriate wmi_cmd_buf
*/
memcpy(...)
complete(&wmi->cmd_wait)
/* awakened by the bogus callback
* => invalid return result
*/
mutex_unlock(&wmi->op_mutex)
return 0

To fix this, move 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@syzkaller.appspotmail.com
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
---
v2: do not extract ath9k_wmi_rsp_callback() internals, rephrase
description

drivers/net/wireless/ath/ath9k/wmi.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
index d652c647d56b..688453a2e53a 100644
--- a/drivers/net/wireless/ath/ath9k/wmi.c
+++ b/drivers/net/wireless/ath/ath9k/wmi.c
@@ -242,10 +242,10 @@ static void ath9k_wmi_ctrl_rx(void *priv, struct sk_buff *skb,
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);
+ spin_unlock_irqrestore(&wmi->wmi_lock, flags);

free_skb:
kfree_skb(skb);
@@ -283,7 +283,8 @@ 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;
@@ -293,6 +294,11 @@ 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);

@@ -333,11 +339,7 @@ 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