[PATCH] nfc: nfcmrvl: validate helper command length before pull

[PATCH] nfc: nfcmrvl: validate helper command length before pull

[Pengpeng Hou]

The firmware download receive path removes the NCI data header and
reads the helper command before validating the remaining packet length.
A short frame can therefore reach the data access before the malformed
packet is rejected.

Validate the complete helper command length before stripping the NCI
data header.

Fixes: 3194c6870158 ("NFC: nfcmrvl: add firmware download support")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 drivers/nfc/nfcmrvl/fw_dnld.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/nfc/nfcmrvl/fw_dnld.c b/drivers/nfc/nfcmrvl/fw_dnld.c
index 2b8f401d8fd7..8b9d5257320d 100644
--- a/drivers/nfc/nfcmrvl/fw_dnld.c
+++ b/drivers/nfc/nfcmrvl/fw_dnld.c
@@ -263,9 +263,14 @@ static int process_state_fw_dnld(struct nfcmrvl_private *priv,
 		 * B8..N: payload
 		 */
 
-		/* Remove NCI HDR */
-		skb_pull(skb, 3);
-		if (skb->data[0] != HELPER_CMD_PACKET_FORMAT || skb->len != 5) {
+		if (skb->len != NCI_DATA_HDR_SIZE + 5) {
+			nfc_err(priv->dev, "bad command");
+			return -EINVAL;
+		}
+
+		/* Remove NCI header */
+		skb_pull(skb, NCI_DATA_HDR_SIZE);
+		if (skb->data[0] != HELPER_CMD_PACKET_FORMAT) {
 			nfc_err(priv->dev, "bad command");
 			return -EINVAL;
 		}
-- 
2.43.0