Re: [PATCH 4.19 01/20] nfc: st21nfca: Fix potential buffer overflows in EVT_TRANSACTION

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> commit 4fbcc1a4cb20fe26ad0225679c536c80f1648221 upstream.
> 
> 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.
> 
> Signed-off-by: Jordy Zomer <jordy@pwning.systems>
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Denis Efremov <denis.e.efremov@oracle.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

It seems that this patch causes an memory leak, transaction does not
seem to be freed in the error paths.

(I also wonder if the skb should be freed in the error paths...?)

Reported-by: <theflamefire89@gmail.com>

>  drivers/nfc/st21nfca/se.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> --- a/drivers/nfc/st21nfca/se.c
> +++ b/drivers/nfc/st21nfca/se.c
> @@ -332,6 +332,11 @@ int st21nfca_connectivity_event_received
>  			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);
>  
> @@ -341,6 +346,11 @@ int st21nfca_connectivity_event_received
>  			return -EPROTO;
>  
>  		transaction->params_len = skb->data[transaction->aid_len + 3];
> +
> +		/* 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;
> +
>  		memcpy(transaction->params, skb->data +
>  		       transaction->aid_len + 4, transaction->params_len);
>  
> 

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