linux-kernel - Re: [PATCH v3 03/11] media: videobuf2: Remove VB2_MAX

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Message-ID: <f21d6fce-155c-28f0-fdea-e9264ba1f7ba@xs4all.nl>
Date:   Fri, 23 Jun 2023 09:02:26 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Dan Carpenter <dan.carpenter@...aro.org>
Cc:     mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
        ming.qian@....com, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        nicolas.dufresne@...labora.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v3 03/11] media: videobuf2: Remove VB2_MAX_FRAME limit on
 buffer storage

On 22/06/2023 16:13, Benjamin Gaignard wrote:
> 
> Le 22/06/2023 à 16:11, Dan Carpenter a écrit :
>> On Thu, Jun 22, 2023 at 03:13:41PM +0200, Benjamin Gaignard wrote:
>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>>> index f1ff7af34a9f..86e1e926fa45 100644
>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>>> @@ -455,9 +455,9 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>>>       struct vb2_buffer *vb;
>>>       int ret;
>>>   -    /* Ensure that q->num_buffers+num_buffers is below VB2_MAX_FRAME */
>>> +    /* Ensure that q->num_buffers + num_buffers is UINT_MAX */
>>>       num_buffers = min_t(unsigned int, num_buffers,
>>> -                VB2_MAX_FRAME - q->num_buffers);
>>> +                UINT_MAX - q->num_buffers);
>>>         for (buffer = 0; buffer < num_buffers; ++buffer) {
>>>           /* Allocate vb2 buffer structures */
>> Ah...  Here's one of the integer overflow bugs I was talking about.  The
>> __vb2_queue_alloc() function returns an int so if num_buffers goes over
>> INT_MAX we are hosed.
> 
> I will limit it to:
> #define VB2_QUEUE_MAX_BUFFERS  (INT_MAX & PAGE_MASK)  /* The mask prevents 85% of integer overflows */
> as you have suggest it.

IMHO INT_MAX is way overkill. How about (1U << 20)? I would like some sort of
sanity check here. 1048576 buffers of 640x480 and 4 bytes per pixel is 1.2 TB.

Since a TB of memory is doable these days, I think this is a reasonable
value for MAX_BUFFERS without allowing just anything.

An alternative is to make this a kernel config.

Regards,

	Hans

> 
> That will be in version 4.
> 
> Thanks,
> Benjamin
> 
>>
>> regards,
>> dan carpenter
>>