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Update draft: addressing AD comments

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Jean-Marc Valin 2017-07-25 23:09:14 -04:00
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doc/draft-ietf-codec-opus-update.xml
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@ -10,7 +10,7 @@
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-codec-opus-update-07"
<rfc category="std" docName="draft-ietf-codec-opus-update-08"
ipr="trust200902" updates="6716">
<front>
<title abbrev="Opus Update">Updates to the Opus Audio Codec</title>
@ -47,7 +47,7 @@
<date day="16" month="July" year="2017" />
<date day="26" month="July" year="2017" />
<abstract>
<t>This document addresses minor issues that were found in the specification
@ -58,8 +58,11 @@
<middle>
<section title="Introduction">
<t>This document addresses minor issues that were discovered in the reference
implementation of the Opus codec that serves as the specification in
<xref target="RFC6716">RFC 6716</xref>. Only issues affecting the decoder are
implementation of the Opus codec. Unlike most IETF specifications, Opus is defined
in <xref target="RFC6716">RFC 6716</xref> in terms of a normative reference
decoder implementation rather than from the associated text description.
That RFC includes the reference decoder implementation as Appendix A.
That's why only issues affecting the decoder are
listed here. An up-to-date implementation of the Opus encoder can be found at
<eref target="https://opus-codec.org/"/>.</t>
<t>
@ -75,7 +78,8 @@
at the end of a line and the white space at the beginning
of the following line are not part of the patch. A properly formatted patch
including all changes is available at
<eref target="https://www.ietf.org/proceedings/98/slides/materials-98-codec-opus-update-00.patch"/>.
<eref target="https://www.ietf.org/proceedings/98/slides/materials-98-codec-opus-update-00.patch"/>
and has a SHA1 029e3aa88fc342c91e67a21e7bfbc9458661cd5f.
</t>
</section>
@ -110,8 +114,8 @@
]]></artwork>
</figure>
<t>
This change affects the normative part of the decoder, although the
amount of change is too small to make a significant impact on testvectors.
This change affects the normative output of the decoder, but the
amount of change is within the tolerance and too small to make the testvector check fail.
</t>
</section>
@ -146,7 +150,7 @@
<t>This packet parsing issue is limited to reading memory up
to about 60 kB beyond the compressed buffer. This can only be triggered
by a compressed packet more than about 16 MB long, so it's not a problem
for RTP. In theory, it <spanx style="emph">could</spanx> crash a file
for RTP. In theory, it could crash a file
decoder (e.g. Opus in Ogg) if the memory just after the incoming packet
is out-of-range, but our attempts to trigger such a crash in a production
application built using an affected version of the Opus decoder failed.</t>
@ -159,19 +163,19 @@
local buffer was opus_int16.</t>
<t>Because the size was wrong, this potentially allowed the source
and destination regions of the memcpy() to overlap.
We <spanx style="emph">believe</spanx> that nSamplesIn is at least fs_in_khZ,
We believe that nSamplesIn (number of input samples) is at least fs_in_khZ (sampling rate in kHz),
which is at least 8.
Since RESAMPLER_ORDER_FIR_12 is only 8, that should not be a problem once
the type size is fixed.</t>
<t>The size of the buffer used RESAMPLER_MAX_BATCH_SIZE_IN, but the
data stored in it was actually _twice_ the input batch size
data stored in it was actually twice the input batch size
(nSamplesIn&lt;&lt;1).</t>
</list></t>
<t>
The fact that the code never produced any error in testing (including when run under the
Valgrind memory debugger), suggests that in practice
the batch sizes are reasonable enough that none of the issues above
was ever a problem. However, proving that is non-obvious.
was ever a problem. However, the authors know of no obvious approach to proving that.
</t>
<t>The code can be fixed by applying the following changes to line 78 of silk/resampler_private_IIR_FIR.c:
</t>
@ -266,7 +270,7 @@ rc_mult2 ), mult2Q);
</figure>
</section>
<section title="Integer wrap-around in LSF decoding">
<section title="Integer wrap-around in LSF decoding" anchor="lsf_overflow">
<t>
It was discovered -- also from decoder fuzzing -- that an integer wrap-around could
occur when decoding line spectral frequency coefficients from extreme bitstreams.
@ -294,7 +298,7 @@ silk_ADD_SAT16( NLSF_Q15[i-1], NDeltaMin_Q15[i] ) );
<section title="Cap on Band Energy">
<t>On extreme bit-streams, it is possible for log-domain band energy levels
to exceed the maximum single-precision floating point value once converted
to a linear scale. This would later cause the decoded values to be NaN,
to a linear scale. This would later cause the decoded values to be NaN (not a number),
possibly causing problems in the software using the PCM values. This can be
avoided with the following patch to line 552 of celt/quant_bands.c:
</t>
@ -318,7 +322,7 @@ silk_ADD_SAT16( NLSF_Q15[i-1], NDeltaMin_Q15[i] ) );
enough bits to code a single CELT band (8 - 9.6 kHz). When that happens,
the second band (CELT band 18, from 9.6 to 12 kHz) cannot use folding
because it is wider than the amount already coded, and falls back to
LCG noise. Because it can also happen on transients (e.g. stops), it
white noise. Because it can also happen on transients (e.g. stops), it
can cause audible pre-echo.
</t>
<t>
@ -424,11 +428,67 @@ effective_lowband+N);
</t>
<t>The new test vectors are located at
<eref target="https://www.ietf.org/proceedings/98/slides/materials-98-codec-opus-newvectors-00.tar.gz"/>.
The SHA1 hash of the test vectors are:
<figure>
<artwork>
<![CDATA[
e49b2862ceec7324790ed8019eb9744596d5be01 testvector01.bit
b809795ae1bcd606049d76de4ad24236257135e0 testvector02.bit
e0c4ecaeab44d35a2f5b6575cd996848e5ee2acc testvector03.bit
a0f870cbe14ebb71fa9066ef3ee96e59c9a75187 testvector04.bit
9b3d92b48b965dfe9edf7b8a85edd4309f8cf7c8 testvector05.bit
28e66769ab17e17f72875283c14b19690cbc4e57 testvector06.bit
bacf467be3215fc7ec288f29e2477de1192947a6 testvector07.bit
ddbe08b688bbf934071f3893cd0030ce48dba12f testvector08.bit
3932d9d61944dab1201645b8eeaad595d5705ecb testvector09.bit
521eb2a1e0cc9c31b8b740673307c2d3b10c1900 testvector10.bit
6bc8f3146fcb96450c901b16c3d464ccdf4d5d96 testvector11.bit
338c3f1b4b97226bc60bc41038becbc6de06b28f testvector12.bit
f5ef93884da6a814d311027918e9afc6f2e5c2c8 testvector01.dec
48ac1ff1995250a756e1e17bd32acefa8cd2b820 testvector02.dec
d15567e919db2d0e818727092c0af8dd9df23c95 testvector03.dec
1249dd28f5bd1e39a66fd6d99449dca7a8316342 testvector04.dec
b85675d81deef84a112c466cdff3b7aaa1d2fc76 testvector05.dec
55f0b191e90bfa6f98b50d01a64b44255cb4813e testvector06.dec
61e8b357ab090b1801eeb578a28a6ae935e25b7b testvector07.dec
a58539ee5321453b2ddf4c0f2500e856b3966862 testvector08.dec
bb96aad2cde188555862b7bbb3af6133851ef8f4 testvector09.dec
1b6cdf0413ac9965b16184b1bea129b5c0b2a37a testvector10.dec
b1fff72b74666e3027801b29dbc48b31f80dee0d testvector11.dec
98e09bbafed329e341c3b4052e9c4ba5fc83f9b1 testvector12.dec
1e7d984ea3fbb16ba998aea761f4893fbdb30157 testvector01m.dec
48ac1ff1995250a756e1e17bd32acefa8cd2b820 testvector02m.dec
d15567e919db2d0e818727092c0af8dd9df23c95 testvector03m.dec
1249dd28f5bd1e39a66fd6d99449dca7a8316342 testvector04m.dec
d70b0bad431e7d463bc3da49bd2d49f1c6d0a530 testvector05m.dec
6ac1648c3174c95fada565161a6c78bdbe59c77d testvector06m.dec
fc5e2f709693738324fb4c8bdc0dad6dda04e713 testvector07m.dec
aad2ba397bf1b6a18e8e09b50e4b19627d479f00 testvector08m.dec
6feb7a7b9d7cdc1383baf8d5739e2a514bd0ba08 testvector09m.dec
1b6cdf0413ac9965b16184b1bea129b5c0b2a37a testvector10m.dec
fd3d3a7b0dfbdab98d37ed9aa04b659b9fefbd18 testvector11m.dec
98e09bbafed329e341c3b4052e9c4ba5fc83f9b1 testvector12m.dec
]]>
</artwork>
</figure>
Note that the decoder input bitstream files (.bit) are unchanged.
</t>
</section>
<section anchor="security" title="Security Considerations">
<t>This document adds no new security considerations on top of
<t>This document fixes two security issues reported on Opus and that affect the
reference implementation in <xref target="RFC6716">RFC 6716</xref>: CVE-2013-0899
<eref target="https://nvd.nist.gov/vuln/detail/CVE-2013-0899"/>
and CVE-2017-0381 <eref target="https://nvd.nist.gov/vuln/detail/CVE-2017-0381"/>.
CVE-2013-0899 is fixed by <xref target="padding"/> and
could theoretically cause information leak, but the
leaked information would at the very least go through the decoder process before
being accessible to the attacker. Also, the bug can only be triggered by Opus packets
at least 24 MB in size. CVE-2017-0381 is fixed by <xref target="lsf_overflow"/> and, as far
as the authors are aware, could not be exploited in any way (despite the claims in
the CVE) unless the read-only table
was somehow placed very close to sensitive data, which is highly unlikely.
Beyond the two fixed CVEs, this document adds no new security considerations on top of
<xref target="RFC6716">RFC 6716</xref>.
</t>
</section>
@ -442,7 +502,8 @@ effective_lowband+N);
<section anchor="Acknowledgements" title="Acknowledgements">
<t>We would like to thank Juri Aedla for reporting the issue with the parsing of
the Opus padding. Also, thanks to Jonathan Lennox and Mark Harris for their
the Opus padding. Thanks to Felicia Lim for reporting the LSF integer overflow issue.
Also, thanks to Tina le Grand, Jonathan Lennox, and Mark Harris for their
feedback on this document.</t>
</section>
</middle>