From:   Jordy Zomer <jordy@pwning.systems>
To:     linux-kernel@vger.kernel.org
Cc:     Jordy Zomer <jordy@pwning.systems>,
        Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org
Subject: [PATCH] nfc: st21nfca: Fix potential buffer overflows in EVT_TRANSACTION
Date:   Wed, 17 Nov 2021 18:17:03 +0100
Message-Id: <20211117171706.2731410-1-jordy@pwning.systems>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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 :)

Signed-off-by: Jordy Zomer <jordy@pwning.systems>
---
 drivers/nfc/st21nfca/se.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/nfc/st21nfca/se.c b/drivers/nfc/st21nfca/se.c
index a43fc4117fa5..e3483aca3280 100644
--- a/drivers/nfc/st21nfca/se.c
+++ b/drivers/nfc/st21nfca/se.c
@@ -316,6 +316,11 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
 			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);
 
@@ -325,6 +330,14 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
 			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