linux-kernel - Re: NULL pointer dereference in iio_buffer

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Date:	Tue, 31 Jul 2012 14:42:37 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Fengguang Wu <fengguang.wu@...el.com>
CC:	Jonathan Cameron <jic23@...nel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: NULL pointer dereference in iio_buffer_register()

On 07/31/2012 12:31 PM, Fengguang Wu wrote:
>> [    7.623739] BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
> 
> I managed to root cause it:
> 
>         [    2.108085] BUG: unable to handle kernel NULL pointer dereference at 00000060
>         [    2.112015] EIP: [<c19b4f4f>] iio_buffer_register+0x1f/0x360 SS:ESP 0068:ce837f34
> 
>         $ addr2line -e vmlinux -i c19b4f4f
>         /c/wfg/linux/drivers/iio/industrialio-buffer.c:275
> 
>         (gdb) p &((struct iio_buffer *) 0)->attrs
>         $1 = (const struct attribute_group **) 0x60
> 
> The panic happens while trying to dereference the NULL indio_dev->buffer:
> 
>         266 int iio_buffer_register(struct iio_dev *indio_dev,
>         267                         const struct iio_chan_spec *channels,
>         268                         int num_channels)
>         269 {  
>         270         struct iio_dev_attr *p;
>         271         struct attribute **attr;
>         272         struct iio_buffer *buffer = indio_dev->buffer;
>         273         int ret, i, attrn, attrcount, attrcount_orig = 0;
>         274 
> ==>     275         if (buffer->attrs)
>         276                 indio_dev->groups[indio_dev->groupcounter++] = buffer->attrs;
> 
> iio_dummy_probe() has the code to configure that buffer, however
> iio_simple_dummy_configure_buffer() is defined to do nothing on
> !CONFIG_IIO_SIMPLE_DUMMY_BUFFER..
> 
>         448         /* Configure buffered capture support. */
> ==>     449         ret = iio_simple_dummy_configure_buffer(indio_dev);
>         450         if (ret < 0)
>         451                 goto error_unregister_events;
>         452 
>         453         /*
>         454          * Register the channels with the buffer, but avoid the output
>         455          * channel being registered by reducing the number of channels by 1.
>         456          */
>         457         ret = iio_buffer_register(indio_dev, iio_dummy_channels, 5);
>         458         if (ret < 0)
>         459                 goto error_unconfigure_buffer;
> 
> Any ideas to fix it?
> 

Hi,

I think the best would be to move the iio_buffer_register to
iio_simple_dummy_configure_buffer.

- Lars
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