[PATCH 3/4] wifi: mt76: mt7925: fix potential tx_retries underflow

[Ryder Lee]

When FIELD_GET returns 0 for the retry count, subtracting 1 causes
an unsigned integer underflow, resulting in tx_retries becoming a
very large value (0xFFFFFFFF for u32).

Fix by checking if count is non-zero before subtracting 1.

Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Ryder Lee <ryder.lee at mediatek.com>
---
 drivers/net/wireless/mediatek/mt76/mt7925/mac.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
index c47bd812b..c56a9e530 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
@@ -1141,8 +1141,9 @@ mt7925_mac_tx_free(struct mt792x_dev *dev, void *data, int len)
 
 		if (info & MT_TXFREE_INFO_HEADER) {
 			if (wcid) {
-				wcid->stats.tx_retries +=
-					FIELD_GET(MT_TXFREE_INFO_COUNT, info) - 1;
+				u32 count = FIELD_GET(MT_TXFREE_INFO_COUNT, info);
+
+				wcid->stats.tx_retries += count ? count - 1 : 0;
 				wcid->stats.tx_failed +=
 					!!FIELD_GET(MT_TXFREE_INFO_STAT, info);
 			}
-- 
2.45.2