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Message-Id: <20220329175431.3175472-1-mfaltesek@google.com>
Date: Tue, 29 Mar 2022 12:54:31 -0500
From: Martin Faltesek <mfaltesek@...omium.org>
To: netdev@...r.kernel.org, krzk@...nel.org,
christophe.ricard@...il.com, jordy@...ing.systems
Cc: sameo@...ux.intel.com, wklin@...gle.com, groeck@...gle.com,
surenb@...gle.com, mfaltesek@...gle.com, gregkh@...uxfoundation.org
Subject: [PATCH] nfc: st21nfca: Refactor EVT_TRANSACTION
EVT_TRANSACTION has four different bugs:
1. First conditional has logical AND but should be OR. It should
always check if it isn't NFC_EVT_TRANSACTION_AID_TAG, then
bail.
2. Potential under allocating memory:devm_kzalloc (skb->len - 2)
when the aid_len specified in the packet is less than the fixed
NFC_MAX_AID_LENGTH in struct nfc_evt_transaction. In addition,
aid_len is u32 in the data structure, and u8 in the packet,
under counting 3 more bytes.
3. Memory leaks after kzalloc when returning error.
4. The final conditional check is also incorrect, for the same reasons
explained in #2.
Fixes: 26fc6c7f02cb ("NFC: st21nfca: Add HCI transaction event support")
Fixes: 4fbcc1a4cb20 ("nfc: st21nfca: Fix potential buffer overflows in EVT_TRANSACTION")
Signed-off-by: Martin Faltesek <mfaltesek@...gle.com>
---
drivers/nfc/st21nfca/se.c | 65 ++++++++++++++++++++++++++-------------
1 file changed, 43 insertions(+), 22 deletions(-)
diff --git a/drivers/nfc/st21nfca/se.c b/drivers/nfc/st21nfca/se.c
index c922f10d0d7b..acc8d831246a 100644
--- a/drivers/nfc/st21nfca/se.c
+++ b/drivers/nfc/st21nfca/se.c
@@ -292,6 +292,8 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
int r = 0;
struct device *dev = &hdev->ndev->dev;
struct nfc_evt_transaction *transaction;
+ u32 aid_len;
+ u8 params_len;
pr_debug("connectivity gate event: %x\n", event);
@@ -306,37 +308,56 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
* Description Tag Length
* AID 81 5 to 16
* PARAMETERS 82 0 to 255
+ *
+ * The key differences are aid storage length is variably sized
+ * in the packet, but fixed in nfc_evt_transaction, and that the aid_len
+ * is u8 in the packet, but u32 in the structure, and the tags in
+ * the packet are not part of nfc_evt_transaction.
+ *
+ * size in bytes: 1 1 5-16 1 1 0-255
+ * offset: 1 2 aid_len + 2 aid_len + 3 aid_len + 4
+ * member name : aid_tag(M) aid_len aid params_tag(M) params_len params
+ * example : 0x81 5-16 X 0x82 0-255 X
*/
- if (skb->len < NFC_MIN_AID_LENGTH + 2 &&
- skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
- return -EPROTO;
-
- transaction = devm_kzalloc(dev, skb->len - 2, GFP_KERNEL);
- if (!transaction)
- return -ENOMEM;
- transaction->aid_len = skb->data[1];
+ /*
+ * Validate the packet is large enough to read the first two bytes
+ * containing the aid_tag and aid_len, and then read both. Capacity
+ * checks are expanded incrementally after this, for clarity.
+ */
+ if (skb->len < 2 || skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
+ return -EPROTO;
- /* Checking if the length of the AID is valid */
- if (transaction->aid_len > sizeof(transaction->aid))
- return -EINVAL;
+ aid_len = skb->data[1];
+ /*
+ * With the actual aid_len, verify there is enough space in
+ * the packet to read params_tag and params_len, and that
+ * aid_len does not exceed destination capacity. Reference
+ * offset comment above for +4 +3 +2 offsets used.
+ */
+ if (skb->len < aid_len + 4 || aid_len > sizeof(transaction->aid))
+ return -EPROTO;
- memcpy(transaction->aid, &skb->data[2],
- transaction->aid_len);
+ params_len = skb->data[aid_len + 3];
- /* Check next byte is PARAMETERS tag (82) */
- if (skb->data[transaction->aid_len + 2] !=
- NFC_EVT_TRANSACTION_PARAMS_TAG)
+ /*
+ * Verify PARAMETERS tag is (82), and final validation that enough
+ * space in packet to read everything.
+ */
+ if ((skb->data[aid_len + 2] != NFC_EVT_TRANSACTION_PARAMS_TAG) ||
+ (skb->len < aid_len + 4 + params_len))
return -EPROTO;
- transaction->params_len = skb->data[transaction->aid_len + 3];
+ transaction = devm_kzalloc(dev, sizeof(struct nfc_evt_transaction) +
+ params_len, GFP_KERNEL);
+ if (!transaction)
+ return -ENOMEM;
- /* Total size is allocated (skb->len - 2) minus fixed array members */
- if (transaction->params_len > ((skb->len - 2) - sizeof(struct nfc_evt_transaction)))
- return -EINVAL;
+ transaction->aid_len = aid_len;
+ transaction->params_len = params_len;
- memcpy(transaction->params, skb->data +
- transaction->aid_len + 4, transaction->params_len);
+ memcpy(transaction->aid, &skb->data[2], aid_len);
+ memcpy(transaction->params, &skb->data[aid_len + 4], params_len);
r = nfc_se_transaction(hdev->ndev, host, transaction);
break;
--
2.35.1.1021.g381101b075-goog
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