On Tue, Nov 20, 2018 at 12:03:31PM +0100, Tomas Härdin wrote: > tis 2018-11-20 klockan 00:04 +0100 skrev Michael Niedermayer: > > On Mon, Nov 19, 2018 at 09:37:28AM +0100, Tomas Härdin wrote: > > > mån 2018-11-19 klockan 02:02 +0100 skrev Michael Niedermayer: > > > > On Sun, Nov 18, 2018 at 11:32:21PM +0100, Tomas Härdin wrote: > > > > > lör 2018-11-17 klockan 03:01 +0100 skrev Michael Niedermayer: > > > > > > Fixes: > > > > > > 11295/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TRUEMOTION2_fuzzer-4888953459572736 > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > > > > > > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > > > > > > > > > > > --- > > > > > > libavcodec/truemotion2.c | 6 +++--- > > > > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > > > > > > > diff --git a/libavcodec/truemotion2.c b/libavcodec/truemotion2.c > > > > > > index 58a577f53c..c583ff4032 100644 > > > > > > --- a/libavcodec/truemotion2.c > > > > > > +++ b/libavcodec/truemotion2.c > > > > > > @@ -484,7 +484,7 @@ static inline void tm2_high_chroma(int *data, > > > > > > int stride, int *last, unsigned *C > > > > > > } > > > > > > } > > > > > > > > > > > > -static inline void tm2_low_chroma(int *data, int stride, int > > > > > > *clast, int *CD, int *deltas, int bx) > > > > > > +static inline void tm2_low_chroma(int *data, int stride, int > > > > > > *clast, unsigned *CD, int *deltas, int bx) > > > > > > { > > > > > > int t; > > > > > > int l; > > > > > > @@ -494,8 +494,8 @@ static inline void tm2_low_chroma(int *data, > > > > > > int stride, int *clast, int *CD, in > > > > > > prev = clast[-3]; > > > > > > else > > > > > > prev = 0; > > > > > > - t = (CD[0] + CD[1]) >> 1; > > > > > > - l = (prev - CD[0] - CD[1] + clast[1]) >> 1; > > > > > > + t = (int)(CD[0] + CD[1]) >> 1; > > > > > > > > > > I presume the old code would overflow for sums exceeding INT_MAX. > > > > > > > > There were overflows in the sense of undefined behavior, yes > > > > > > > > > > > > > Why > > > > > then is there a cast to int before the shift and not after? > > > > > > > > because shifts of signed and unsigned values produce different results > > > > > > > > maybe the unsigned type confused you. CD is signed in a semantic sense > > > > its > > > > stored in a unsigned type because otherwise this code has undefined > > > > behavior. > > > > It would be better to use a type with different name but that had lead > > > > to > > > > long arguments that went nowhere in the past. So i tend to use plain > > > > unsigned now for these kind of cases as it seems that is what most > > > > people > > > > prefer. > > > > > > So signed overflow is intended? Huh, weird format. > > > > it occurs in the fuzzed sample used here. i do not know if it occurs in > > normal samples, i would suspect it does not. > > I see. Some kind of spec might be nice, but I suspect the spec as it is > is named Kostya
yes, probably ... will apply thanks [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB While the State exists there can be no freedom; when there is freedom there will be no State. -- Vladimir Lenin
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