Re: spi: imx: initialize usedma earlier

[Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>]

On Wed, Mar 16, 2016 at 10:42:38AM +0300, Dan Carpenter wrote:
> Hello Sascha Hauer,
> 
> This is a semi-automatic email about new static checker warnings.
> 
> The patch c008a8007162: "spi: imx: initialize usedma earlier" from
> Feb 24, 2016, leads to the following Smatch complaint:
> 
> drivers/spi/spi-imx.c:870 spi_imx_setupxfer()
> 	 error: we previously assumed 't' could be null (see line 848)
> 
> drivers/spi/spi-imx.c
>    847	
>    848		config.bpw = t ? t->bits_per_word : spi->bits_per_word;
>                              ^
>    849		config.speed_hz  = t ? t->speed_hz : spi->max_speed_hz;
>                                    ^
> Old code checks for NULL.
> 
>    850		config.mode = spi->mode;
>    851		config.cs = spi->chip_select;
>    852	
>    853		if (!config.speed_hz)
>    854			config.speed_hz = spi->max_speed_hz;
>    855		if (!config.bpw)
>    856			config.bpw = spi->bits_per_word;
>    857	
>    858		/* Initialize the functions for transfer */
>    859		if (config.bpw <= 8) {
>    860			spi_imx->rx = spi_imx_buf_rx_u8;
>    861			spi_imx->tx = spi_imx_buf_tx_u8;
>    862		} else if (config.bpw <= 16) {
>    863			spi_imx->rx = spi_imx_buf_rx_u16;
>    864			spi_imx->tx = spi_imx_buf_tx_u16;
>    865		} else {
>    866			spi_imx->rx = spi_imx_buf_rx_u32;
>    867			spi_imx->tx = spi_imx_buf_tx_u32;
>    868		}
>    869	
>    870		if (spi_imx_can_dma(spi_imx->bitbang.master, spi, t))
>                                                                   ^
> Patch adds a new unchecked dereference (inside the function call).

This really is a possible NULL pointer dereference. From what I see
spi_imx_setupxfer() should be called with a NULL transfer during setup
of a new SPI slave device. Apparently this doesn't happen because
otherwise I should have seen a crash on every boot with this patch
applied. Anyway, just sent a patch to fix this.

Sascha

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