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

[Ivan Kalvachev]

On 6/9/17, wm4 <nfxjfg at googlemail.com> wrote:
> On Fri, 9 Jun 2017 00:10:49 +0200
> Michael Niedermayer <michael at niedermayer.cc> wrote:
>
>> On Sat, May 27, 2017 at 12:24:16PM +0200, wm4 wrote:
>> > On Sat, 27 May 2017 03:56:42 +0200
>> > Michael Niedermayer <michael at niedermayer.cc> wrote:
>> >
>> > > On Fri, May 26, 2017 at 07:06:44PM -0400, Ronald S. Bultje wrote:
>> > > > Hi,
>> > > >
>> > > > On Fri, May 26, 2017 at 6:34 PM, Michael Niedermayer
>> > > > <michael at niedermayer.cc
>> > > > > wrote:
>> > > >
>> > > > > On Fri, May 26, 2017 at 06:07:35PM -0400, Ronald S. Bultje wrote:
>> > > > >
>> > > > > > 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.
>> > > > >
>> > > > > please calm down, you make all kinds of statments and implications
>> > > > > in
>> > > > > the text above which are not true.
>> > > > >
>> > > > > This specific code in git triggers undefined behavior, the patch
>> > > > > fixes
>> > > > > this undefined behavior.
>> > > > > If that is exploitable (which i neither claim it is nor that it
>> > > > > isnt)
>> > > > > its a issue that exists before the patch but not afterwards.
>> > > >
>> > > >
>> > >
>> > > > *unsigned* removes the exploit. SUINT keeps it, and is therefore
>> > > > part of a
>> > > > rootkit.
>> > >
>> > > SUINT is defined to unsigned, if unsigned removes the issue
>> > > so does SUINT.
>> >
>> > Then why is it called SUINT and not UINT.
>>
>> Signed value in
>> Unsigned
>> INTeger type
>>
>> This concept is needed for fixing undefined operations efficiently.
>> The type can always be replaced by unsigned and thats what is being
>> done now.
>> But it makes the code hard to understand and maintain because these
>> values are not positive integers but signed integers. Which for
>> C standard compliance need to be stored in a unsigned type.
>>
>> Both SUINT and unsigned should produce identical binaries but unsigned
>
> Is that so? Then please add a FATE check that guarantees this.
>
>> is semantically wrong.
>
> If it's wrong then it shouldn't be used.

I think you should read (again) these articles:
http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html