Re: [PATCH net-next] net: ena: fix unintended sign extension

From: David Miller
Date: Thu Oct 18 2018 - 00:48:20 EST

From: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>
Date: Fri, 12 Oct 2018 21:49:48 +0200

> In the following expression:
> 372 size = io_sq->bounce_buf_ctrl.buffer_size *
> 373 io_sq->bounce_buf_ctrl.buffers_num;
> both buffer_size and buffers_num are of type u16 (16 bits, unsigned),
> so they are promoted to type int (32 bits, signed) and then
> sign-extended to type size_t.
> Fix this by casting io_sq->bounce_buf_ctrl.buffer_size to size_t in
> order to avoid the sign extension and unintended results.
> Addresses-Coverity-ID: 1474187 ("Unintended sign extension")
> Addresses-Coverity-ID: 1474189 ("Unintended sign extension")
> Fixes: 689b2bdaaa14 ("net: ena: add functions for handling Low Latency Queues in ena_com")
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

I don't understand how this can possibly be a real problem, and it looks
therefore like we are just papering over a coverity warning.

I'm not applying this without more information and justification.