Re: [PATCH v1] can: mcp251xfd: Add some sysfs debug interfaces for registers r/w

[knigh dark]

Vincent MAILHOL <mailhol.vincent@xxxxxxxxxx> 于2021年1月22日周五 下午4:51写道：
>
> Hi,
>
> In addition to Marc’s comment, I also have security concerns.
>
> On Fri. 22 Jan 2021 at 15:22, Su Yanjun <suyanjun218@xxxxxxxxx> wrote:
> > When i debug mcp2518fd, some method to track registers is
> > needed. This easy debug interface will be ok.
> >
> > For example,
> > read a register at 0xe00:
> > echo 0xe00 > can_get_reg
> > cat can_get_reg
> >
> > write a register at 0xe00:
> > echo 0xe00,0x60 > can_set_reg
>
> What about:
> printf "A%0.s" {1..1000} > can_set_reg
>
> Doesn’t it crash the kernel?
I check the input buffer in __get_param with 16 bytes limit.
Thanks for your review.
>
> I see no checks of the buf len in your code and I suspect it to be
> vulnerable to stack buffer overflow exploits.
>
> > Signed-off-by: Su Yanjun <suyanjun218@xxxxxxxxx>
> > ---
> >  .../net/can/spi/mcp251xfd/mcp251xfd-core.c    | 132 ++++++++++++++++++
> >  1 file changed, 132 insertions(+)
> >
> > diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> > index ab8aad0a7594..d65abe5505d5 100644
> > --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> > +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> > @@ -27,6 +27,131 @@
> >
> >  #define DEVICE_NAME "mcp251xfd"
> >
> > +/* Add sysfs debug interface for easy to debug
> > + *
> > + * For example,
> > + *
> > + * - read a register
> > + * echo 0xe00 > can_get_reg
> > + * cat can_get_reg
> > + *
> > + * - write a register
> > + * echo 0xe00,0x1 > can_set_reg
> > + *
> > + */
> > +static int reg_offset;
> > +
> > +static int __get_param(const char *buf, char *off, char *val)
> > +{
> > +       int len;
> > +
> > +       if (!buf || !off || !val)
> > +               return -EINVAL;
> > +
> > +       len = 0;
> > +       while (*buf != ',') {
> > +               *off++ = *buf++;
> > +               len++;
> > +
> > +               if (len >= 16)
> > +                       return -EINVAL;
> > +       }
> > +
> > +       buf++;
> > +
> > +       *off = '\0';
> > +
> > +       len = 0;
> > +       while (*buf) {
> > +               *val++ = *buf++;
> > +               len++;
> > +
> > +               if (len >= 16)
> > +                       return -EINVAL;
> > +       }
> > +
> > +       *val = '\0';
> > +
> > +       return 0;
> > +}
> > +
> > +static ssize_t can_get_reg_show(struct device *dev,
> > +                               struct device_attribute *attr, char *buf)
> > +{
> > +       int err;
> > +       u32 val;
> > +       struct mcp251xfd_priv *priv;
> > +
> > +       priv = dev_get_drvdata(dev);
> > +
> > +       err = regmap_read(priv->map_reg, reg_offset, &val);
> > +       if (err)
> > +               return 0;
> > +
> > +       return sprintf(buf, "reg = 0x%08x, val = 0x%08x\n", reg_offset, val);
> > +}
> > +
> > +static ssize_t can_get_reg_store(struct device *dev,
> > +                                struct device_attribute *attr, const char *buf, size_t len)
> > +{
> > +       u32 off;
> > +
> > +       reg_offset = 0;
> > +
> > +       if (kstrtouint(buf, 0, &off) || (off % 4))
> > +               return -EINVAL;
> > +
> > +       reg_offset = off;
> > +
> > +       return len;
> > +}
> > +
> > +static ssize_t can_set_reg_show(struct device *dev,
> > +                               struct device_attribute *attr, char *buf)
> > +{
> > +       return 0;
> > +}
> > +
> > +static ssize_t can_set_reg_store(struct device *dev,
> > +                                struct device_attribute *attr, const char *buf, size_t len)
> > +{
> > +       struct mcp251xfd_priv *priv;
> > +       u32 off, val;
> > +       int err;
> > +
> > +       char s1[16];
> > +       char s2[16];
> > +
> > +       if (__get_param(buf, s1, s2))
> > +               return -EINVAL;
> > +
> > +       if (kstrtouint(s1, 0, &off) || (off % 4))
> > +               return -EINVAL;
> > +
> > +       if (kstrtouint(s2, 0, &val))
> > +               return -EINVAL;
> > +
> > +       err = regmap_write(priv->map_reg, off, val);
> > +       if (err)
> > +               return -EINVAL;
> > +
> > +       return len;
> > +}
> > +
> > +static DEVICE_ATTR_RW(can_get_reg);
> > +static DEVICE_ATTR_RW(can_set_reg);
> > +
> > +static struct attribute *can_attributes[] = {
> > +       &dev_attr_can_get_reg.attr,
> > +       &dev_attr_can_set_reg.attr,
> > +       NULL
> > +};
> > +
> > +static const struct attribute_group can_group = {
> > +       .attrs = can_attributes,
> > +       NULL
> > +};
> > +
> >  static const struct mcp251xfd_devtype_data mcp251xfd_devtype_data_mcp2517fd = {
> >         .quirks = MCP251XFD_QUIRK_MAB_NO_WARN | MCP251XFD_QUIRK_CRC_REG |
> >                 MCP251XFD_QUIRK_CRC_RX | MCP251XFD_QUIRK_CRC_TX |
> > @@ -2944,6 +3069,12 @@ static int mcp251xfd_probe(struct spi_device *spi)
> >         if (err)
> >                 goto out_free_candev;
> >
> > +       err = sysfs_create_group(&spi->dev.kobj, &can_group);
> > +       if (err) {
> > +               netdev_err(priv->ndev, "Create can group fail.\n");
> > +               goto out_free_candev;
> > +       }
> > +
> >         err = can_rx_offload_add_manual(ndev, &priv->offload,
> >                                         MCP251XFD_NAPI_WEIGHT);
> >         if (err)
> > @@ -2972,6 +3103,7 @@ static int mcp251xfd_remove(struct spi_device *spi)
> >         mcp251xfd_unregister(priv);
> >         spi->max_speed_hz = priv->spi_max_speed_hz_orig;
> >         free_candev(ndev);
> > +       sysfs_remove_group(&spi->dev.kobj, &can_group);
> >
> >         return 0;
> >  }
> > --
> > 2.25.1
> >