linux-kernel - [mfd] question about potential null pointer dereference

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Date:   Tue, 23 May 2017 16:33:41 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     patches@...nsource.wolfsonmicro.com, linux-kernel@...r.kernel.org
Subject: [mfd] question about potential null pointer dereference


Hello everybody,

While looking into Coverity ID 1408830 I ran into the following piece  
of code at drivers/mfd/wm831x-spi.c:26

  26static int wm831x_spi_probe(struct spi_device *spi)
  27{
  28        struct wm831x_pdata *pdata = dev_get_platdata(&spi->dev);
  29        const struct spi_device_id *id = spi_get_device_id(spi);
  30        const struct of_device_id *of_id;
  31        struct wm831x *wm831x;
  32        enum wm831x_parent type;
  33        int ret;
  34
  35        if (spi->dev.of_node) {
  36                of_id = of_match_device(wm831x_of_match, &spi->dev);
  37                type = (enum wm831x_parent)of_id->data;
  38        } else {
  39                type = (enum wm831x_parent)id->driver_data;
  40        }
  41
  42        wm831x = devm_kzalloc(&spi->dev, sizeof(struct wm831x),  
GFP_KERNEL);
  43        if (wm831x == NULL)
  44                return -ENOMEM;
  45
  46        spi->mode = SPI_MODE_0;
  47
  48        spi_set_drvdata(spi, wm831x);
  49        wm831x->dev = &spi->dev;
  50        wm831x->type = type;
  51
  52        wm831x->regmap = devm_regmap_init_spi(spi, &wm831x_regmap_config);
  53        if (IS_ERR(wm831x->regmap)) {
  54                ret = PTR_ERR(wm831x->regmap);
  55                dev_err(wm831x->dev, "Failed to allocate register  
map: %d\n",
  56                        ret);
  57                return ret;
  58        }
  59
  60        if (pdata)
  61                memcpy(&wm831x->pdata, pdata, sizeof(*pdata));
  62
  63        return wm831x_device_init(wm831x, spi->irq);
  64}

The issue here is that there is a potential NULL pointer dereference  
at line 37, in case function of_match_device() returns NULL.

Maybe a patch like the following could be applied in order to avoid  
any chance of a NULL pointer dereference:

index c332e28..7b227c9 100644
--- a/drivers/mfd/wm831x-spi.c
+++ b/drivers/mfd/wm831x-spi.c
@@ -34,6 +34,10 @@ static int wm831x_spi_probe(struct spi_device *spi)

         if (spi->dev.of_node) {
                 of_id = of_match_device(wm831x_of_match, &spi->dev);
+               if (!of_id) {
+                       dev_err(&spi->dev, "Failed to find matching id\n");
+                       return -EINVAL;
+               }
                 type = (enum wm831x_parent)of_id->data;
         } else {
                 type = (enum wm831x_parent)id->driver_data;

What do you think?

I'd really appreciate any comment on this.

Thank you!
--
Gustavo A. R. Silva