[PATCH v2] nfc: st-nci: Fix potential buffer overflows in EVT_TRANSACTION

[Jordy Zomer]

It appears that there are some buffer overflows in EVT_TRANSACTION.
This happens because the length parameters that are passed to memcpy
come directly from skb->data and are not guarded in any way.

It would be nice if someone can review and test this patch because
I don't own the hardware :)

EDIT: Changed comment style and double newlines

Signed-off-by: Jordy Zomer <jordy@pwning.systems>
---
 drivers/nfc/st-nci/se.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/nfc/st-nci/se.c b/drivers/nfc/st-nci/se.c
index 7764b1a4c3cf..8e2ac8a3d199 100644
--- a/drivers/nfc/st-nci/se.c
+++ b/drivers/nfc/st-nci/se.c
@@ -335,6 +335,11 @@ static int st_nci_hci_connectivity_event_received(struct nci_dev *ndev,
 			return -ENOMEM;
 
 		transaction->aid_len = skb->data[1];
+
+		/* Checking if the length of the AID is valid */
+		if (transaction->aid_len > sizeof(transaction->aid))
+			return -EINVAL;
+
 		memcpy(transaction->aid, &skb->data[2], transaction->aid_len);
 
 		/* Check next byte is PARAMETERS tag (82) */
@@ -343,6 +348,16 @@ static int st_nci_hci_connectivity_event_received(struct nci_dev *ndev,
 			return -EPROTO;
 
 		transaction->params_len = skb->data[transaction->aid_len + 3];
+
+		/*
+		 * check if the length of the parameters is valid
+		 * we can't use sizeof(transaction->params) because it's
+		 * a flexible array member so we have to check if params_len
+		 * is bigger than the space allocated for the array
+		 */
+		if (transaction->params_len > ((skb->len - 2) - sizeof(struct nfc_evt_transaction)))
+			return -EINVAL;
+
 		memcpy(transaction->params, skb->data +
 		       transaction->aid_len + 4, transaction->params_len);
 
-- 
2.27.0