net: ena: Fix potential sign extension issue

Small unsigned types are promoted to larger signed types in
the case of multiplication, the result of which may overflow.
In case the result of such a multiplication has its MSB
turned on, it will be sign extended with '1's.
This changes the multiplication result.

Code example of the phenomenon:
-------------------------------
u16 x, y;
size_t z1, z2;

x = y = 0xffff;
printk("x=%x y=%x\n",x,y);

z1 = x*y;
z2 = (size_t)x*y;

printk("z1=%lx z2=%lx\n", z1, z2);

Output:
-------
x=ffff y=ffff
z1=fffffffffffe0001 z2=fffe0001

The expected result of ffff*ffff is fffe0001, and without the
explicit casting to avoid the unwanted sign extension we got
fffffffffffe0001.

This commit adds an explicit casting to avoid the sign extension
issue.

Fixes: 689b2bdaaa14 ("net: ena: add functions for handling Low Latency Queues in ena_com")
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 9e9e4a03f1a8c9bd4c8d68cb20340157c4547e80..2d8a66ea82fab7f0a023ab469ccc33321d0b4ba3 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -351,7 +351,7 @@ 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);