Re: [PATCH] nfc: Fix the sockaddr length sanitization in llcp_sock_connect

[Samuel Ortiz]

Hi Mateusz,

On Wed, May 24, 2017 at 12:26:20PM +0200, Mateusz Jurczyk wrote:
> Fix the sockaddr length verification in the connect() handler of NFC/LLCP
> sockets, to compare against the size of the actual structure expected on
> input (sockaddr_nfc_llcp) instead of its shorter version (sockaddr_nfc).
> 
> Both structures are defined in include/uapi/linux/nfc.h. The fields
> specific to the _llcp extended struct are as follows:
> 
>    276		__u8 dsap; /* Destination SAP, if known */
>    277		__u8 ssap; /* Source SAP to be bound to */
>    278		char service_name[NFC_LLCP_MAX_SERVICE_NAME]; /* Service name URI */;
>    279		size_t service_name_len;
> 
> If the caller doesn't provide a sufficiently long sockaddr buffer, these
> fields remain uninitialized (and they currently originate from the stack
> frame of the top-level sys_connect handler). They are then copied by
> llcp_sock_connect() into internal storage (nfc_llcp_sock structure), and
> could be subsequently read back through the user-mode getsockname()
> function (handled by llcp_sock_getname()). This would result in the
> disclosure of up to ~70 uninitialized bytes from the kernel stack to
> user-mode clients capable of creating AFC_NFC sockets.
> 
> Signed-off-by: Mateusz Jurczyk <mjurczyk@xxxxxxxxxx>
> ---
>  net/nfc/llcp_sock.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
Applied to nfc-next, thanks.

Cheers,
Samuel.