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

[Carl Eugen Hoyos <ceffmpeg@gmail.com>]

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Am Fr., 2. Sept. 2022 um 09:04 Uhr schrieb Anton Khirnov <anton@khirnov.net>:
>
> 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.

Definitely, new patch attached.

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

I was unable to reproduce with 8-bit input.

Thank you, Carl Eugen

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From 062b8a3a202f72125fa05582c2a3c0abc8305887 Mon Sep 17 00:00:00 2001
From: Carl Eugen Hoyos <ceffmpeg@gmail.com>
Date: Sat, 3 Sep 2022 22:50:19 +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 | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/libavfilter/vf_rotate.c b/libavfilter/vf_rotate.c
index 4429e3d543..96c250a459 100644
--- a/libavfilter/vf_rotate.c
+++ b/libavfilter/vf_rotate.c
@@ -258,8 +258,8 @@ static uint8_t *interpolate_bilinear16(uint8_t *dst_color,
 {
     int int_x = av_clip(x>>16, 0, max_x);
     int int_y = av_clip(y>>16, 0, max_y);
-    int frac_x = x&0xFFFF;
-    int frac_y = y&0xFFFF;
+    int64_t frac_x = x&0xFFFF;
+    int64_t frac_y = y&0xFFFF;
     int i;
     int int_x1 = FFMIN(int_x+1, max_x);
     int int_y1 = FFMIN(int_y+1, max_y);
@@ -269,10 +269,10 @@ 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 = (((1<<16) - frac_x)*s00 + frac_x*s01);
+        int64_t s1 = (((1<<16) - frac_x)*s10 + frac_x*s11);
 
-        AV_WL16(&dst_color[i], ((int64_t)((1<<16) - frac_y)*s0 + (int64_t)frac_y*s1) >> 32);
+        AV_WL16(&dst_color[i], (((1<<16) - frac_y)*s0 + frac_y*s1) >> 32);
     }
 
     return dst_color;
-- 
2.17.1


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