51 lines
2.5 KiB
Diff
51 lines
2.5 KiB
Diff
From 4174c26e0aaab19d01afdea0a46f7f95fdc6b3e6 Mon Sep 17 00:00:00 2001
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From: "Timothy B. Terriberry" <tterribe@xiph.org>
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Date: Tue, 13 Oct 2020 12:30:41 -0700
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Subject: [PATCH] Fix short-circuit test when seeking in short files
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When a file is very, very short (i.e., only one packet) and uses
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end-trimming, the apparent granule position preceding the first
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sample in the first packet can underflow.
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We were computing this value by subtracting the packet duration
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from the computed per-packet granule position and expecting this
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computation to always succeed.
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Because it could fail in the presence of end-trimming on the first
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packet (ironically, exactly the situation where the short-circuit
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is helpful), it would leave the value uninitialized, and then use
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it in a comparison, which is undefined behavior.
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The correct solution is to check for failure and force the previous
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page's granule position to 0 in this case.
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---
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src/opusfile.c | 15 +++++++++++++--
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1 file changed, 13 insertions(+), 2 deletions(-)
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diff --git a/src/opusfile.c b/src/opusfile.c
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index 0d09e97..5bf9f91 100644
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--- a/src/opusfile.c
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+++ b/src/opusfile.c
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@@ -2358,8 +2358,19 @@ static int op_pcm_seek_page(OggOpusFile *_of,
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For very small files (with all of the data in a single page,
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generally 1 second or less), we can loop them continuously
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without seeking at all.*/
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- OP_ALWAYS_TRUE(!op_granpos_add(&prev_page_gp,_of->op[0].granulepos,
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- -op_get_packet_duration(_of->op[0].packet,_of->op[0].bytes)));
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+ if(op_granpos_add(&prev_page_gp,_of->op[0].granulepos,
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+ -op_get_packet_duration(_of->op[0].packet,_of->op[0].bytes))<0) {
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+ /*We validate/sanitize the per-packet timestamps, so the only way
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+ we should fail to calculate a granule position for the
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+ previous page is if the first page with completed packets in
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+ the stream is also the last, and end-trimming causes the
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+ apparent granule position preceding the first sample in the
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+ first packet to underflow.
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+ The starting PCM offset is then 0 by spec mandate (see also:
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+ op_find_initial_pcm_offset()).*/
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+ OP_ASSERT(_of->op[0].e_o_s);
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+ prev_page_gp=0;
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+ }
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if(op_granpos_cmp(prev_page_gp,_target_gp)<=0){
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/*Don't call op_decode_clear(), because it will dump our
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packets.*/
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--
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2.30.0
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