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

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

[Gustavo A. R. Silva]

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@embeddedor.com>
---
 drivers/net/ethernet/amazon/ena/ena_com.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 420cede..9a8130e 100644
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -369,7 +369,7 @@ static int ena_com_init_io_sq(struct ena_com_dev *ena_dev,
 			ENA_COM_BOUNCE_BUFFER_CNTRL_CNT;
 		io_sq->bounce_buf_ctrl.next_to_use = 0;
 
-		size = io_sq->bounce_buf_ctrl.buffer_size *
+		size = (size_t)io_sq->bounce_buf_ctrl.buffer_size *
 			 io_sq->bounce_buf_ctrl.buffers_num;
 
 		dev_node = dev_to_node(ena_dev->dmadev);
-- 
2.7.4

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

[David Miller]

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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@embeddedor.com>

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.