Re: NFC: st21nfca: Add HCI transaction event support

[Dan Carpenter <dan.carpenter@oracle.com>]

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