[PATCH 1/2] wifi: mt76: usb: fix source overread in mt76u_copy

[Jiale Yao]

mt76u_copy() rounds up len to a multiple of four and uses the rounded
length as the bound for memcpy() from the source buffer. When the
caller's length is not four-byte aligned, the final copy reads up to
three bytes past the source buffer.

Keep the original length for the source copy and zero the remaining
bytes in the transmit buffer so that the hardware access width remains
four-byte aligned.

Fixes: 9446248669968 ("mt76: speed up usb bulk copy")
Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
---
 drivers/net/wireless/mediatek/mt76/usb.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index a9af3aa6b80a..a42a33f4e907 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -171,8 +171,10 @@ static void mt76u_copy(struct mt76_dev *dev, u32 offset,
 {
 	struct mt76_usb *usb = &dev->usb;
 	const u8 *val = data;
-	int ret;
 	int current_batch_size;
+	int len_aligned;
+	int copy_len;
+	int ret;
 	int i = 0;
 
 	/* Assure that always a multiple of 4 bytes are copied,
@@ -180,12 +182,16 @@ static void mt76u_copy(struct mt76_dev *dev, u32 offset,
 	 * See: "mt76: round up length on mt76_wr_copy"
 	 * Commit 850e8f6fbd5d0003b0
 	 */
-	len = round_up(len, 4);
+	len_aligned = round_up(len, 4);
 
 	mutex_lock(&usb->usb_ctrl_mtx);
-	while (i < len) {
-		current_batch_size = min_t(int, usb->data_len, len - i);
-		memcpy(usb->data, val + i, current_batch_size);
+	while (i < len_aligned) {
+		current_batch_size = min_t(int, usb->data_len, len_aligned - i);
+		copy_len = min_t(int, current_batch_size, len - i);
+		memcpy(usb->data, val + i, copy_len);
+		if (copy_len < current_batch_size)
+			memset(usb->data + copy_len, 0,
+			       current_batch_size - copy_len);
 		ret = __mt76u_vendor_request(dev, MT_VEND_MULTI_WRITE,
 					     USB_DIR_OUT | USB_TYPE_VENDOR,
 					     0, offset + i, usb->data,
-- 
2.34.1