[FFmpeg-devel] [PATCH] avcodec/fft_template: Fix multiple runtime error: signed integer overflow: -1943918714 - 1935113003 cannot be represented in type 'int'

[Ronald S. Bultje]

Hi,

On Fri, May 26, 2017 at 5:50 PM, Michael Niedermayer <michael at niedermayer.cc
> wrote:

> On Fri, May 26, 2017 at 11:18:12PM +0200, Hendrik Leppkes wrote:
> > On Fri, May 26, 2017 at 11:11 PM, Michael Niedermayer
> > <michael at niedermayer.cc> wrote:
> > > On Fri, May 26, 2017 at 03:20:14PM +0100, Rostislav Pehlivanov wrote:
> > >> On 26 May 2017 at 12:21, wm4 <nfxjfg at googlemail.com> wrote:
> > >>
> > >> > On Thu, 25 May 2017 16:10:49 +0200
> > >> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> > >> >
> > >> > > Fixes: 1735/clusterfuzz-testcase-minimized-5350472347025408
> > >> > >
> > >> > > Found-by: continuous fuzzing process
> https://github.com/google/oss-
> > >> > fuzz/tree/master/projects/ffmpeg
> > >> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > >> > > ---
> > >> > >  libavcodec/fft_template.c | 50 +++++++++++++++++++++++-------
> > >> > -----------------
> > >> > >  1 file changed, 25 insertions(+), 25 deletions(-)
> > >> > >
> > >> > > diff --git a/libavcodec/fft_template.c b/libavcodec/fft_template.c
> > >> > > index 480557f49f..e3a37e5d69 100644
> > >> > > --- a/libavcodec/fft_template.c
> > >> > > +++ b/libavcodec/fft_template.c
> > >> > > @@ -249,7 +249,7 @@ static void fft_calc_c(FFTContext *s,
> FFTComplex *z)
> > >> > {
> > >> > >
> > >> > >      int nbits, i, n, num_transforms, offset, step;
> > >> > >      int n4, n2, n34;
> > >> > > -    FFTSample tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7, tmp8;
> > >> > > +    SUINT tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7, tmp8;
> > >> >
> > >> > I want this SUINT thing gone, not have more of it.
> > >> > _______________________________________________
> > >> > ffmpeg-devel mailing list
> > >> > ffmpeg-devel at ffmpeg.org
> > >> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > >> >
> > >>
> > >> I agree, especially here.
> > >
> > >> Overflows should be left to happen in transforms if the input is
> corrupt.
> > >
> > > signed int overflow is not allowed in C, if that is what you meant.
> > >
> > >
> >
> > Its "undefined", which means what the result will be is not defined -
> > which in such a DSP function is irrelevant, if all it causes is
> > corrupt output ... from corrupt input.
>
> no, this is not correct.
> undefined behavior does not mean the effect will be limited to
> the output.
> It could cause the process to hard lockup, trigger an exception or
> set a flag causing errors in later unrelated code.


We've discussed this before, if you believe this to be exploitable, why
allow it in our repository at all? I know of no other project that even
remotely allows such ridiculous things. Please limit exploitable code to
your personal tree, ffmpeg is not a rootkit.

Ronald