Re: [PATCH v3 03/11] media: videobuf2: Remove VB2_MAX_FRAME limit on buffer storage

[Benjamin Gaignard]

Le 23/06/2023 à 09:02, Hans Verkuil a écrit :
> 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.

I will go for (1U << 20) in next version.

Regards,
Benjamin

> 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