From: Felix Fietkau <nbd@nbd.name>
Date: Tue, 17 Sep 2024 11:09:42 +0000 (+0200)
Subject: wifi: mt76: do not increase mcu skb refcount if retry is not supported
X-Git-Tag: v6.12-rc6~33^2~24^2~15
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=34b69548108480ebb36cb6a067974a88ec745897;p=thirdparty%2Flinux.git

wifi: mt76: do not increase mcu skb refcount if retry is not supported

If mcu_skb_prepare_msg is not implemented, incrementing skb refcount does not
work for mcu message retry. In some cases (e.g. on SDIO), shared skbs can trigger
a BUG_ON, crashing the system.
Fix this by only incrementing refcount if retry is actually supported.

Fixes: 3688c18b65ae ("wifi: mt76: mt7915: retry mcu messages")
Closes: https://lore.kernel.org/r/d907b13a-f8be-4cb8-a0bb-560a21278041@notapiano/
Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> #KernelCI
Tested-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240917110942.22077-1-nbd@nbd.name
---

diff --git a/drivers/net/wireless/mediatek/mt76/mcu.c b/drivers/net/wireless/mediatek/mt76/mcu.c
index 98da82b74094d..3353012e85429 100644
--- a/drivers/net/wireless/mediatek/mt76/mcu.c
+++ b/drivers/net/wireless/mediatek/mt76/mcu.c
@@ -84,13 +84,16 @@ int mt76_mcu_skb_send_and_get_msg(struct mt76_dev *dev, struct sk_buff *skb,
 	mutex_lock(&dev->mcu.mutex);
 
 	if (dev->mcu_ops->mcu_skb_prepare_msg) {
+		orig_skb = skb;
 		ret = dev->mcu_ops->mcu_skb_prepare_msg(dev, skb, cmd, &seq);
 		if (ret < 0)
 			goto out;
 	}
 
 retry:
-	orig_skb = skb_get(skb);
+	/* orig skb might be needed for retry, mcu_skb_send_msg consumes it */
+	if (orig_skb)
+		skb_get(orig_skb);
 	ret = dev->mcu_ops->mcu_skb_send_msg(dev, skb, cmd, &seq);
 	if (ret < 0)
 		goto out;
@@ -105,7 +108,7 @@ retry:
 	do {
 		skb = mt76_mcu_get_response(dev, expires);
 		if (!skb && !test_bit(MT76_MCU_RESET, &dev->phy.state) &&
-		    retry++ < dev->mcu_ops->max_retry) {
+		    orig_skb && retry++ < dev->mcu_ops->max_retry) {
 			dev_err(dev->dev, "Retry message %08x (seq %d)\n",
 				cmd, seq);
 			skb = orig_skb;