Hi Marcel
On Fri, Dec 20, 2013 at 2:36 PM, Marcel Holtmann <mar...@holtmann.org> wrote:
> Hi David,
>
>> HID core expects the input buffers to be at least of size 4096
>> (HID_MAX_BUFFER_SIZE). Other sizes will result in buffer-overflows if an
>> input-report is smaller than advertised. We could, like i2c, compute the
>> biggest report-size instead of using HID_MAX_BUFFER_SIZE, but this will
>> blow up if report-descriptors are changed after ->start() has been called.
>> So lets be safe and just use the biggest buffer we have.
>>
>> Note that this adds an additional copy to the HIDP input path. If there is
>> a way to make sure the skb-buf is big enough, we should use that instead.
>>
>> The best way would be to make hid-core honor the @size argument, though,
>> that sounds easier than it is. So lets just fix the buffer-overflows for
>> now and afterwards look for a faster way for all transport drivers.
>>
>> Signed-off-by: David Herrmann <dh.herrm...@gmail.com>
>> ---
>> Hi
>>
>> Any ideas how to improve this patch? I'd like to avoid the extra copy but I
>> have
>> no clue how the skb stuff works exactly.
>
> the buffers are coming straight from L2CAP. They might come in fragments. We
> have to reassemble them and while there are large packets for sure, we rather
> not want to allocate 4096 for every reassembled packet to make HID happy.
>
> I am not super familiar with the underlying memory management of SKBs, but I
> assume they use slices of some sort internally. So uses large SKBs for 20
> byte HID report will cause an issue with all other protocols running on top
> of L2CAP
I was more thinking of an skb call to increase the underlying buffer
of a single package. We could call this together with skb_linearize()
in HIDP to guarantee the skb-buf is big enough. Technically, this will
probably result in the same behavior as my own patch so probably not
the way to go.
>> I also haven't figured out a nice way to make HID-core honor the "size"
>> parameter. hid-input depends on getting the whole input-report.
>
> I think this needs clearly fixing.
And we have a volunteer, yippie! ;)
I think hid_input_report() in hid-core.c is the only place that relies
on this. Maybe it really is easier to fix it. But I am not even
slightly familiar with that code. So if no-one of the HID core
developers steps up to fix it, we should take the transport-driver
fixes instead. As nearly all transport-drivers are affected by this,
maybe we should even move this buffer into hid_device and provide
hid_input_truncated_report() which does this.
Anyhow, waiting for Jiri's comments on this.
>> Comments welcome!
>> David
>>
>> net/bluetooth/hidp/core.c | 16 ++++++++++++++--
>> net/bluetooth/hidp/hidp.h | 4 ++++
>> 2 files changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
>> index 292e619..d9fb934 100644
>> --- a/net/bluetooth/hidp/core.c
>> +++ b/net/bluetooth/hidp/core.c
>> @@ -430,6 +430,16 @@ static void hidp_del_timer(struct hidp_session *session)
>> del_timer(&session->timer);
>> }
>>
>> +static void hidp_process_report(struct hidp_session *session,
>> + int type, const u8 *data, int len, int intr)
>> +{
>> + if (len > HID_MAX_BUFFER_SIZE)
>> + len = HID_MAX_BUFFER_SIZE;
>> +
>> + memcpy(session->input_buf, data, len);
>> + hid_input_report(session->hid, type, session->input_buf, len, intr);
>> +}
>> +
>> static void hidp_process_handshake(struct hidp_session *session,
>> unsigned char param)
>> {
>> @@ -502,7 +512,8 @@ static int hidp_process_data(struct hidp_session
>> *session, struct sk_buff *skb,
>> hidp_input_report(session, skb);
>>
>> if (session->hid)
>> - hid_input_report(session->hid, HID_INPUT_REPORT,
>> skb->data, skb->len, 0);
>> + hidp_process_report(session, HID_INPUT_REPORT,
>> + skb->data, skb->len, 0);
>> break;
>>
>> case HIDP_DATA_RTYPE_OTHER:
>> @@ -584,7 +595,8 @@ static void hidp_recv_intr_frame(struct hidp_session
>> *session,
>> hidp_input_report(session, skb);
>>
>> if (session->hid) {
>> - hid_input_report(session->hid, HID_INPUT_REPORT,
>> skb->data, skb->len, 1);
>> + hidp_process_report(session, HID_INPUT_REPORT,
>> + skb->data, skb->len, 1);
>> BT_DBG("report len %d", skb->len);
>> }
>> } else {
>> diff --git a/net/bluetooth/hidp/hidp.h b/net/bluetooth/hidp/hidp.h
>> index ab52414..8798492 100644
>> --- a/net/bluetooth/hidp/hidp.h
>> +++ b/net/bluetooth/hidp/hidp.h
>> @@ -24,6 +24,7 @@
>> #define __HIDP_H
>>
>> #include <linux/types.h>
>> +#include <linux/hid.h>
>> #include <linux/kref.h>
>> #include <net/bluetooth/bluetooth.h>
>> #include <net/bluetooth/l2cap.h>
>> @@ -179,6 +180,9 @@ struct hidp_session {
>>
>> /* Used in hidp_output_raw_report() */
>> int output_report_success; /* boolean */
>> +
>> + /* temporary input buffer */
>> + u8 input_buf[HID_MAX_BUFFER_SIZE];
>> };
>
> The report does not need any specific alignment?
This is already aligned to native size, isn't it? Anyhow, HID core
does not have any alignment-restrictions I am aware of. Jiri? I
thought the extract()/implement() stuff was fixed recently.
Thanks
David
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