Re: [PATCH v2 1/5] HID: intel_ish-hid: fix potential uninitialized data usage

On Mon, May 22, 2017 at 9:17 PM, Srinivas Pandruvada
[off-list ref] wrote:

Hi Arnd,
On Thu, 2017-05-18 at 22:21 +0200, Arnd Bergmann wrote:

quoted

gcc points out an uninialized pointer dereference that could happen
if we ever get to recv_ishtp_cl_msg_dma() or recv_ishtp_cl_msg()
with an empty &dev->read_list:

drivers/hid/intel-ish-hid/ishtp/client.c: In function
'recv_ishtp_cl_msg_dma':
drivers/hid/intel-ish-hid/ishtp/client.c:1049:3: error: 'cl' may be
used uninitialized in this function [-Werror=maybe-uninitialized]

The warning only appeared in very few randconfig builds, as the
spinlocks tend to prevent gcc from tracing the variables. I only
saw it in configurations that had neither SMP nor LOCKDEP enabled.

As we can see, we only enter the case if 'complete_rb' is non-NULL,
and then 'cl' is known to point to complete_rb->cl. Adding another
initialization to the same pointer is harmless here and makes it
clear to the compiler that the behavior is well-defined.

Did you get chance to test these changes on a platform with ISH?

No, I only build-tested it and though about the fix carefully.

        Arnd