I never got a response on this. Is this remote exploitable or from the
firmware?
regards,
dan carpenter
On Tue, Feb 10, 2015 at 12:00:51PM +0300, Dan Carpenter wrote:
> Hello Christophe Ricard,
>
> The patch 26fc6c7f02cb: "NFC: st21nfca: Add HCI transaction event
> support" from Feb 1, 2015, leads to the following static checker
> warning:
>
> drivers/nfc/st21nfca/st21nfca_se.c:321 st21nfca_connectivity_event_received()
> error: 'skb->data[1]' from user is not capped properly
>
> drivers/nfc/st21nfca/st21nfca_se.c
> 300 int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
> 301 u8 event, struct sk_buff *skb)
> 302 {
> 303 int r = 0;
> 304 struct device *dev = &hdev->ndev->dev;
> 305 struct nfc_evt_transaction *transaction;
> 306
> 307 pr_debug("connectivity gate event: %x\n", event);
> 308
> 309 switch (event) {
> 310 case ST21NFCA_EVT_CONNECTIVITY:
> 311 break;
> 312 case ST21NFCA_EVT_TRANSACTION:
> 313 if (skb->len < NFC_MIN_AID_LENGTH + 2 &&
> 314 skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
> 315 return -EPROTO;
>
> Here we don't trust skb->data[0].
>
> 316
> 317 transaction = (struct nfc_evt_transaction *)devm_kzalloc(dev,
> 318 skb->len - 2, GFP_KERNEL);
> 319
> 320 transaction->aid_len = skb->data[1];
> 321 memcpy(transaction->aid, &skb->data[2], skb->data[1]);
> ^^^^^^^^^^^^
> But here we trust skb->data[1].
>
> NFC code is hard to analyze because sometimes skb->data[] comes from the
> firmware and holds trusted values. But sometimes it comes from the
> network and can overflow. Smatch marks it all as untrusted so it causes
> a lot of false postives.
>
> Some of them have comments like:
>
> net/nfc/hci/core.c:218 nfc_hci_cmd_received()
> error: buffer overflow 'hdev->pipes' 127 <= 255
>
> But this one doesn't have a comment so it's hard for me as an outsider
> to say if this is a bug or not.
>
> 322
>
> regards,
> dan carpenter
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