wifi: mt76: mt7996: fix potential tx_retries underflow

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: 2461599f835e ("wifi: mt76: mt7996: get tx_retries and tx_failed from txfree")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Link: https://patch.msgid.link/20260605113306.3485554-4-ryder.lee@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>

diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
index 83e8e1e7feb4a006a21c21b7849bf8ba6646fc36..0eebc8182ca9aa02214923489732df281a29011a 100644 (file)
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
@@ -1359,13 +1359,13 @@ next:
                                cur_info++;
                        continue;
                } else if (info & MT_TXFREE_INFO_HEADER) {
-                       u32 tx_retries = 0, tx_failed = 0;
+                       u32 tx_retries = 0, tx_failed = 0, count;
 
                        if (!wcid)
                                continue;
 
-                       tx_retries =
-                               FIELD_GET(MT_TXFREE_INFO_COUNT, info) - 1;
+                       count = FIELD_GET(MT_TXFREE_INFO_COUNT, info);
+                       tx_retries = count ? count - 1 : 0;
                        tx_failed = tx_retries +
                                !!FIELD_GET(MT_TXFREE_INFO_STAT, info);