Re: libnsgif and memory bombs

Here's a better version of the patch:

https://github.com/libvips/libvips/blob/master/libvips/foreign/libnsgif/patches/delay-alloc.patch

(removes a stray create_bitmap call)


On Fri, 2 Apr 2021 at 11:58, <jcupitt@gmail.com> wrote:
>
> Hi all,
>
> I had a thought regarding memory allocation in libnsgif.
>
> At the moment, calling `gif_initialise()` will parse the GIF file and
> allocate memory for rendering. You then call gif_decode_frame() to
> decompress and render each frame of the animation.
>
> However, this means just opening the GIF can trigger very large memory
> allocations, with no chance for the caller to intervene, except by
> putting a hard pixel limit into the bitmap_create() callback. For
> example, a 20 byte GIF can cause a 17gb malloc.
>
> How about delaying the allocation of the bitmap until the first call
> to gif_decode_frame()? This would allow the caller to check the
> detected width and height and apply some kind of size policy before
> allowing rendering to occur.
>
> Here's a possible patch that does this. It's very simple and does not
> affect the API, just the memory behaviour (I think):
>
> https://github.com/libvips/libvips/commit/9bdf5e8cda3e0c63584984282b1e36d97c50bb1a
>
> John
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