From 155e3003d1e614f85566b636973df7118e1b4851 Mon Sep 17 00:00:00 2001 From: Chris Lu Date: Mon, 17 Aug 2026 17:53:31 +0800 Subject: [PATCH] Bluetooth: btmtksdio: Take exclusive ownership of the SKB before TX btmtksdio_tx_packet() prepends the MediaTek SDIO header with skb_push() and writes into that space after only checking the headroom size. On a cloned SKB that headroom belongs to a buffer shared with the other owner, which the driver has no right to write to. Cloned SKBs do reach this path: hci_send_cmd_sync() keeps a clone of every HCI command in hdev->sent_cmd before handing the SKB to the driver, and l2cap_ertm_send() clones SKBs for retransmission. Replace the open-coded headroom check with skb_cow_head(), which both guarantees the headroom and reallocates a private buffer when the SKB is cloned. The cost is one reallocation and copy per cloned packet, the usual price of this pattern in network drivers. This has no observable effect on its own, as the driver only writes in front of skb->data where no other owner looks. It is a prerequisite for "Bluetooth: btmtksdio: Fix out-of-bounds DMA read in the TX path", which writes padding behind skb->tail, and carries the same Fixes: tag so that both are backported together. Fixes: 9aebfd4a2200 ("Bluetooth: mediatek: add support for MediaTek MT7663S and MT7668S SDIO devices") Signed-off-by: Chris Lu Assisted-by: Claude:claude-opus-5 Signed-off-by: Luiz Augusto von Dentz --- drivers/bluetooth/btmtksdio.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/drivers/bluetooth/btmtksdio.c b/drivers/bluetooth/btmtksdio.c index 4e1012e90979..8052e24d503b 100644 --- a/drivers/bluetooth/btmtksdio.c +++ b/drivers/bluetooth/btmtksdio.c @@ -274,13 +274,12 @@ static int btmtksdio_tx_packet(struct btmtksdio_dev *bdev, struct mtkbtsdio_hdr *sdio_hdr; int err; - /* Make sure that there are enough rooms for SDIO header */ - if (unlikely(skb_headroom(skb) < sizeof(*sdio_hdr))) { - err = pskb_expand_head(skb, sizeof(*sdio_hdr), 0, - GFP_ATOMIC); - if (err < 0) - return err; - } + /* Make sure that the data buffer is not shared with anyone else and + * that there is enough room for the SDIO header + */ + err = skb_cow_head(skb, sizeof(*sdio_hdr)); + if (err < 0) + return err; /* Prepend MediaTek SDIO Specific Header */ skb_push(skb, sizeof(*sdio_hdr));