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    SubjectRe: [PATCH] media:usb:cpia2: Properly check framebuffer mmap offsets
    On Mon, Nov 11, 2019 at 05:29:07PM +0100, Greg Kroah-Hartman wrote:
    > On Mon, Nov 11, 2019 at 06:24:42PM +0000, Omer Shalev wrote:
    > > On Mon, Nov 11, 2019 at 12:46:15PM +0100, Greg Kroah-Hartman wrote:
    > > > On Sat, Nov 09, 2019 at 12:39:43PM +0100, Hans Verkuil wrote:
    > > > > Hi Greg,
    > > > >
    > > > > On 11/8/19 9:49 PM, Greg Kroah-Hartman wrote:
    > > > > > On Fri, Nov 08, 2019 at 09:50:36PM +0000, Omer Shalev wrote:
    > > > > >> The cpai2 driver's mmap implementation wasn't properly check for all
    > > > > >> possible offset values. Given a huge offset value , the calculation
    > > > > >> start_offset + size can wrap around to a low value and pass the check
    > > > > >
    > > > > > I thought we checked that in the core of the kernel now, to keep all
    > > > > > drivers from not having to do this type of thing (as they obviously all
    > > > > > forgot to.) Why is this still needed here as well?
    > > > >
    > > > > Where is that checked in the core? I couldn't find anything, but I might
    > > > > have been looking in the wrong place.
    > > >
    > > > Sorry, took me a while to find it. Look at be83bbf80682 ("mmap:
    > > > introduce sane default mmap limits") as I think this should handle the
    > > > problem already.
    > > >
    > > > thanks,
    > > >
    > > > greg k-h
    > >
    > > Thanks Greg. But All other drivers I've seen implement it like that: if(size > total_size || offset >
    > > total_size - size). Which I think, is a better way to write this code, and generally more
    > > secure. Plus, no extra code is needed (just changing this line).
    >
    > The point of the above commit that is in the tree is that no driver has
    > to do this check at all, it's already been done before the driver ever
    > gets called, right?
    >
    > So yes, there's lots of history of drivers doing the check themselves
    > (and getting it wrong as you point out), but that should not matter
    > anymore.
    >
    > Can you verify that your change isn't even needed due to the above
    > mentioned core check for valid values?
    >
    > thanks,
    >
    > greg k-h

    Yes I got it , and thanks again. I think that programmatically , its
    better to write that this way, And therefore I suggested this patch.

    thanks,

    Omer

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