linux-kernel - Re: [PATCH v2] i2c-hid: introduce HID over i2c specification implementation

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Date:	Tue, 16 Oct 2012 19:36:20 +0200
From:	Benjamin Tissoires <benjamin.tissoires@...il.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, fabien.andre@...il.com,
	scott.liu@....com.tw, Jean Delvare <khali@...ux-fr.org>,
	JJ Ding <jj_ding@....com.tw>,
	Shubhrajyoti Datta <omaplinuxkernel@...il.com>,
	linux-i2c@...r.kernel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c-hid: introduce HID over i2c specification implementation

Hi Jiri,

On Tue, Oct 16, 2012 at 10:17 AM, Jiri Slaby <jslaby@...e.cz> wrote:
> On 10/15/2012 10:38 PM, Benjamin Tissoires wrote:
>> Notes:
>> {1}: I don't have all the informations in the beginning of the probe function to
>> get the real size I need to allocate. So the behavior is to allocate first a
>> buffer by using HID_MIN_BUFFER_SIZE and once I got the information, I can
>> reallocate the buffer to the right size (in i2c_hid_start).
>
> And there is a bug in this. See below.
>
>> --- /dev/null
>> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> ...
>> +static int i2c_hid_alloc_buffers(struct i2c_hid *ihid)
>> +{
>> +     /* the worst case is computed from the set_report command with a
>> +      * reportID > 15 and the maximum report length */
>> +     int args_len = sizeof(__u8) + /* optional ReportID byte */
>> +                    sizeof(__u16) + /* data register */
>> +                    sizeof(__u16) + /* size of the report */
>> +                    ihid->bufsize; /* report */
>> +
>> +     ihid->inbuf = kzalloc(ihid->bufsize, GFP_KERNEL);
>> +
>> +     if (!ihid->inbuf)
>> +             return -ENOMEM;
>> +
>> +     ihid->argsbuf = kzalloc(args_len, GFP_KERNEL);
>> +
>> +     if (!ihid->argsbuf) {
>> +             kfree(ihid->inbuf);
>> +             return -ENOMEM;
>> +     }
>> +
>> +     ihid->cmdbuf = kzalloc(sizeof(union command) + args_len, GFP_KERNEL);
>> +
>> +     if (!ihid->cmdbuf) {
>> +             kfree(ihid->inbuf);
>> +             kfree(ihid->argsbuf);
>> +             return -ENOMEM;
>> +     }
>> +
>> +     return 0;
>
> If this is called from hid_start and some of the latter allocation fails
> here, you free the buffers appropriately. However if another start
> occurs (e.g. by loading another module for that particular device), it
> will crash, as the buffers will remain unallocated because at this point
> ihid->bufsize == old_bufsize. You should set ihid->bufsize back to
> old_bufsize if i2c_hid_alloc_buffers fails and also set the pointers to
> NULL here.

well spotted, thanks.
I'll change it in v3 then.

Cheers,
Benjamin

>
> regards,
> --
> js
> suse labs
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