Re: [FFmpeg-devel] [PATCH]lavfi/rotate: Fix undefined behaviour

From: Anton Khirnov <anton@khirnov.net>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH]lavfi/rotate: Fix undefined behaviour
Date: Fri, 02 Sep 2022 09:04:19 +0200
Message-ID: <166210225946.3205.13102915136711192823@lain.khirnov.net> (raw)
In-Reply-To: <CAB0OVGpfP9gV-WcLVWUTs3mrb7hVxqd4s+-EAUVRvN0_Qf-pfA@mail.gmail.com>

Quoting Carl Eugen Hoyos (2022-09-01 21:28:08)
> Hi!
> 
> Attached patch fixes ticket #9799.
> 
> Please comment, Carl Eugen
> 
> From 2cce687961c3b56a92d88184269bf9fa075ae297 Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <ceffmpeg@gmail.com>
> Date: Thu, 1 Sep 2022 20:55:54 +0200
> Subject: [PATCH] lavfi/rotate: Avoid undefined behaviour.
> 
> Fixes the following integer overflows:
> libavfilter/vf_rotate.c:273:13: runtime error: signed integer overflow: 92951468 + 2058533568 cannot be represented in type 'int'
> libavfilter/vf_rotate.c:273:37: runtime error: signed integer overflow: 39684 * 54149 cannot be represented in type 'int'
> libavfilter/vf_rotate.c:272:13: runtime error: signed integer overflow: 247587320 + 1900985032 cannot be represented in type 'int'
> libavfilter/vf_rotate.c:272:37: runtime error: signed integer overflow: 42584 * 50430 cannot be represented in type 'int'
> libavfilter/vf_rotate.c:272:50: runtime error: signed integer overflow: 65083 * 52912 cannot be represented in type 'int'
> libavfilter/vf_rotate.c:273:50: runtime error: signed integer overflow: 65286 * 38044 cannot be represented in type 'int'
> 
> Fixes ticket #9799, different output with different compilers.
> ---
>  libavfilter/vf_rotate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavfilter/vf_rotate.c b/libavfilter/vf_rotate.c
> index 4429e3d543..d319dfe3d9 100644
> --- a/libavfilter/vf_rotate.c
> +++ b/libavfilter/vf_rotate.c
> @@ -269,8 +269,8 @@ static uint8_t *interpolate_bilinear16(uint8_t *dst_color,
>          int s01 = AV_RL16(&src[src_linestep * int_x1 + i + src_linesize * int_y ]);
>          int s10 = AV_RL16(&src[src_linestep * int_x  + i + src_linesize * int_y1]);
>          int s11 = AV_RL16(&src[src_linestep * int_x1 + i + src_linesize * int_y1]);
> -        int s0 = (((1<<16) - frac_x)*s00 + frac_x*s01);
> -        int s1 = (((1<<16) - frac_x)*s10 + frac_x*s11);
> +        int64_t s0 = (((int64_t)(1<<16) - frac_x)*s00 + (int64_t)frac_x*s01);
> +        int64_t s1 = (((int64_t)(1<<16) - frac_x)*s10 + (int64_t)frac_x*s11);

Given that the same casts also appear in the AV_WL16 below, it seems
better to just change the types of frac_x/frac_y.

Also, shouldn't the same change be done also to interpolate_bilinear8?

-- 
Anton Khirnov
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