[PATCH v10 1/7] Bluetooth: btmtksdio: Fix DMA out-of-bounds access in TX path

[Chris Lu <chris.lu@mediatek.com>]

btmtksdio_tx_packet() aligns transfer size to 256 bytes using
round_up(), but does not ensure the skb buffer has sufficient space,
causing DMA to read beyond the buffer.

Fix by expanding skb tailroom if needed and zero-filling the padding.

Fixes: 9aebfd4a2200 ("Bluetooth: mediatek: add support for MediaTek MT7663S and MT7668S SDIO devices")
Signed-off-by: Chris Lu <chris.lu@mediatek.com>
---
 drivers/bluetooth/btmtksdio.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/bluetooth/btmtksdio.c b/drivers/bluetooth/btmtksdio.c
index 5b0fab7b89b5..a21edefaca99 100644
--- a/drivers/bluetooth/btmtksdio.c
+++ b/drivers/bluetooth/btmtksdio.c
@@ -272,6 +272,7 @@ static int btmtksdio_tx_packet(struct btmtksdio_dev *bdev,
 			       struct sk_buff *skb)
 {
 	struct mtkbtsdio_hdr *sdio_hdr;
+	unsigned int padded_len, pad_len;
 	int err;
 
 	/* Make sure that there are enough rooms for SDIO header */
@@ -290,18 +291,40 @@ static int btmtksdio_tx_packet(struct btmtksdio_dev *bdev,
 	sdio_hdr->reserved = cpu_to_le16(0);
 	sdio_hdr->bt_type = hci_skb_pkt_type(skb);
 
+	/* Calculate padded length for block-aligned DMA transfer.
+	 * SDIO requires transfers to be block-aligned (MTK_SDIO_BLOCK_SIZE).
+	 * Pad with zeros to prevent DMA from reading beyond skb buffer.
+	 */
+	padded_len = round_up(skb->len, MTK_SDIO_BLOCK_SIZE);
+	pad_len = padded_len - skb->len;
+
+	if (pad_len > 0) {
+		/* Ensure sufficient tailroom for padding */
+		if (unlikely(skb_tailroom(skb) < pad_len)) {
+			err = pskb_expand_head(skb, 0, pad_len, GFP_ATOMIC);
+			if (err < 0)
+				goto err_skb_pull;
+		}
+
+		/* Zero-fill padding to prevent information disclosure */
+		skb_put_zero(skb, pad_len);
+	}
+
 	clear_bit(BTMTKSDIO_HW_TX_READY, &bdev->tx_state);
-	err = sdio_writesb(bdev->func, MTK_REG_CTDR, skb->data,
-			   round_up(skb->len, MTK_SDIO_BLOCK_SIZE));
+	err = sdio_writesb(bdev->func, MTK_REG_CTDR, skb->data, padded_len);
 	if (err < 0)
-		goto err_skb_pull;
+		goto err_skb_trim;
 
-	bdev->hdev->stat.byte_tx += skb->len;
+	/* Record actual transmitted data (excluding padding) */
+	bdev->hdev->stat.byte_tx += le16_to_cpu(sdio_hdr->len);
 
 	kfree_skb(skb);
 
 	return 0;
 
+err_skb_trim:
+	if (pad_len > 0)
+		skb_trim(skb, skb->len - pad_len);
 err_skb_pull:
 	skb_pull(skb, sizeof(*sdio_hdr));
 
-- 
2.45.2