Re: [FFmpeg-devel] [PATCH 1/6] avformat/avidec: support huge durations

[Michael Niedermayer <michael@niedermayer.cc>]

[-- Attachment #1.1: Type: text/plain, Size: 6596 bytes --]

On Tue, Oct 03, 2023 at 08:53:33PM +0200, Michael Niedermayer wrote:
> On Tue, Oct 03, 2023 at 11:10:20AM +0200, Tomas Härdin wrote:
> > mån 2023-10-02 klockan 21:03 +0200 skrev Michael Niedermayer:
> > > On Mon, Oct 02, 2023 at 11:07:47AM +0200, Anton Khirnov wrote:
> > > > Quoting Michael Niedermayer (2023-10-01 00:28:56)
> > > > > On Sat, Sep 30, 2023 at 10:18:38PM +0200, Anton Khirnov wrote:
> > > > > > Quoting Michael Niedermayer (2023-09-30 16:31:43)
> > > > > > > On Sat, Sep 30, 2023 at 04:04:03PM +0200, Michael Niedermayer
> > > > > > > wrote:
> > > > > > > > On Sat, Sep 30, 2023 at 11:35:19AM +0200, Marton Balint
> > > > > > > > wrote:
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > On Sat, 30 Sep 2023, Michael Niedermayer wrote:
> > > > > > > > > 
> > > > > > > > > > Fixes: signed integer overflow: 109817402400 *
> > > > > > > > > > 301990077 cannot be represented in type 'long long'
> > > > > > > > > > Fixes: 51896/clusterfuzz-testcase-minimized-
> > > > > > > > > > ffmpeg_dem_AVI_fuzzer-6706191715139584
> > > > > > > > > > 
> > > > > > > > > > Found-by: continuous fuzzing process
> > > > > > > > > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > > > > > > > > Signed-off-by: Michael Niedermayer
> > > > > > > > > > <michael@niedermayer.cc>
> > > > > > > > > > ---
> > > > > > > > > > libavformat/avidec.c | 12 ++++++++++--
> > > > > > > > > > 1 file changed, 10 insertions(+), 2 deletions(-)
> > > > > > > > > > 
> > > > > > > > > > diff --git a/libavformat/avidec.c
> > > > > > > > > > b/libavformat/avidec.c
> > > > > > > > > > index 00bd7a98a9d..cfc693842b7 100644
> > > > > > > > > > --- a/libavformat/avidec.c
> > > > > > > > > > +++ b/libavformat/avidec.c
> > > > > > > > > > @@ -27,6 +27,7 @@
> > > > > > > > > > #include "libavutil/avstring.h"
> > > > > > > > > > #include "libavutil/opt.h"
> > > > > > > > > > #include "libavutil/dict.h"
> > > > > > > > > > +#include "libavutil/integer.h"
> > > > > > > > > > #include "libavutil/internal.h"
> > > > > > > > > > #include "libavutil/intreadwrite.h"
> > > > > > > > > > #include "libavutil/mathematics.h"
> > > > > > > > > > @@ -476,7 +477,7 @@ static int
> > > > > > > > > > calculate_bitrate(AVFormatContext *s)
> > > > > > > > > >         AVStream *st = s->streams[i];
> > > > > > > > > >         FFStream *const sti = ffstream(st);
> > > > > > > > > >         int64_t duration;
> > > > > > > > > > -        int64_t bitrate;
> > > > > > > > > > +        int64_t bitrate = 0;
> > > > > > > > > > 
> > > > > > > > > >         for (j = 0; j < sti->nb_index_entries; j++)
> > > > > > > > > >             len += sti->index_entries[j].size;
> > > > > > > > > > @@ -484,7 +485,14 @@ static int
> > > > > > > > > > calculate_bitrate(AVFormatContext *s)
> > > > > > > > > >         if (sti->nb_index_entries < 2 || st->codecpar-
> > > > > > > > > > >bit_rate > 0)
> > > > > > > > > >             continue;
> > > > > > > > > >         duration = sti->index_entries[j-1].timestamp -
> > > > > > > > > > sti->index_entries[0].timestamp;
> > > > > > > > > > -        bitrate = av_rescale(8*len, st->time_base.den,
> > > > > > > > > > duration * st->time_base.num);
> > > > > > > > > > +        if (INT64_MAX / duration >= st->time_base.num)
> > > > > > > > > > {
> > > > > > > > > > +            bitrate = av_rescale(8*len, st-
> > > > > > > > > > >time_base.den, duration * st->time_base.num);
> > > > > > > > > 
> > > > > > > > > Why not always use the AVInteger version? This is not
> > > > > > > > > performance sensitive
> > > > > > > > > as far as I see.
> > > > > > > > 
> > > > > > > > We can, i will have to fix the rounding though so it
> > > > > > > > matches av_rescale()
> > > > > > > 
> > > > > > > will apply this with just AVInteger and fixed rounding with
> > > > > > > my next push probably
> > > > > > 
> > > > > > This seems MUCH less readable to me.
> > > > > 
> > > > > we can add a av_rescale_2den()
> > > > 
> > > > Won't av_rescale_q(len, (AVRational){8, duration}, st->time_base)
> > > > achieve the same effect?
> > > 
> > > duration is 64bit AVRational is 32/32 bit, so i would expect that to
> > > not
> > > work.
> > > If duration was fitting in 32bit then duration * st->time_base.num
> > > would not
> > > have overflowed
> > 
> > Maybe we need a 64/64-bit version of AVRational..
> 
> Iam not convinced at this point that we need that.
> But its not hard to do, our AVInteger code will do any size integers by just
> changing a single number.
> 
> The real annoyance is if you have 32/32 and 64/64 rationals then suddenly
> you need many functions to handle both. Sofar only a fuzzed file exceeded
> our 64 * 64 / 64 == 64 * 32/32 * 32/32 rescale in one place
> adding a 64 * 64 / (64 * 64) rescale would fix that one which seems more
> limited in spreading complexity through the codebase

Ill apply this below, because its undefined behavior and needs to be fixed.
If someone has a better solution please replace my code with it.

@@ -476,7 +477,7 @@ static int calculate_bitrate(AVFormatContext *s)
         AVStream *st = s->streams[i];
         FFStream *const sti = ffstream(st);
         int64_t duration;
-        int64_t bitrate;
+        AVInteger bitrate_i, den_i, num_i;

         for (j = 0; j < sti->nb_index_entries; j++)
             len += sti->index_entries[j].size;
@@ -484,9 +485,14 @@ static int calculate_bitrate(AVFormatContext *s)
         if (sti->nb_index_entries < 2 || st->codecpar->bit_rate > 0)
             continue;
         duration = sti->index_entries[j-1].timestamp - sti->index_entries[0].timestamp;
-        bitrate = av_rescale(8*len, st->time_base.den, duration * st->time_base.num);
-        if (bitrate > 0) {
-            st->codecpar->bit_rate = bitrate;
+        den_i = av_mul_i(av_int2i(duration), av_int2i(st->time_base.num));
+        num_i = av_add_i(av_mul_i(av_int2i(8*len), av_int2i(st->time_base.den)), av_shr_i(den_i, 1));
+        bitrate_i = av_div_i(num_i, den_i);
+        if (av_cmp_i(bitrate_i, av_int2i(INT64_MAX)) <= 0) {
+            int64_t bitrate = av_i2int(bitrate_i);
+            if (bitrate > 0) {
+                st->codecpar->bit_rate = bitrate;
+            }
         }
     }
     return 1;

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The bravest are surely those who have the clearest vision
of what is before them, glory and danger alike, and yet
notwithstanding go out to meet it. -- Thucydides

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".