[PATCH] Bluetooth: btnxpuart: Fix out-of-bounds firmware read in nxp_recv_fw_req_v3()

[Maoyi Xie]

During the v3 firmware download the controller sends a v3_data_req with a
32 bit offset and a 16 bit len. nxp_recv_fw_req_v3() checks only the lower
bound of the offset and then sends firmware from that offset.

	nxpdev->fw_dnld_v3_offset = offset - nxpdev->fw_v3_offset_correction;
	serdev_device_write_buf(nxpdev->serdev, nxpdev->fw->data +
				nxpdev->fw_dnld_v3_offset, len);

Nothing checks that fw_dnld_v3_offset + len stays within nxpdev->fw->size, so a
controller that asks for an offset or length past the firmware image makes the
driver read past the end of nxpdev->fw->data and send that memory back over
UART.

nxp_recv_fw_req_v1() already bounds the same write. Add the equivalent check to
the v3 path, reject the request when it falls outside the firmware image, and
zero len on the error path so the fw_v3_prev_sent bookkeeping at free_skb stays
consistent.

Fixes: 689ca16e5232 ("Bluetooth: NXP: Add protocol support for NXP Bluetooth chipsets")
Suggested-by: Neeraj Kale <neeraj.sanjaykale@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>
---
This is the fix for the out of bounds read I reported on linux-bluetooth. Neeraj
confirmed the bug and asked me to send it. The Suggested-by is for his suggestion
to zero len on the reject path, which keeps the fw_v3_prev_sent bookkeeping at
free_skb consistent.

 drivers/bluetooth/btnxpuart.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/bluetooth/btnxpuart.c b/drivers/bluetooth/btnxpuart.c
index e7036a48ce48..6a1cffe08d5f 100644
--- a/drivers/bluetooth/btnxpuart.c
+++ b/drivers/bluetooth/btnxpuart.c
@@ -1267,6 +1267,12 @@ static int nxp_recv_fw_req_v3(struct hci_dev *hdev, struct sk_buff *skb)
 	}
 
 	nxpdev->fw_dnld_v3_offset = offset - nxpdev->fw_v3_offset_correction;
+	if (nxpdev->fw_dnld_v3_offset >= nxpdev->fw->size ||
+	    len > nxpdev->fw->size - nxpdev->fw_dnld_v3_offset) {
+		bt_dev_err(hdev, "FW download out of bounds, ignoring request");
+		len = 0;
+		goto free_skb;
+	}
 	serdev_device_write_buf(nxpdev->serdev, nxpdev->fw->data +
 				nxpdev->fw_dnld_v3_offset, len);
 
-- 
2.34.1