62 lines
2.4 KiB
Diff
62 lines
2.4 KiB
Diff
From b07b105d1b66e32760095e3602261738443b9e13 Mon Sep 17 00:00:00 2001
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From: Mark Wielaard <mark@klomp.org>
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Date: Wed, 3 Jul 2019 01:28:11 +0200
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Subject: Accept as many selectors as the file format allows.
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But ignore any larger than the theoretical maximum, BZ_MAX_SELECTORS.
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The theoretical maximum number of selectors depends on the maximum
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blocksize (900000 bytes) and the number of symbols (50) that can be
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encoded with a different Huffman tree. BZ_MAX_SELECTORS is 18002.
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But the bzip2 file format allows the number of selectors to be encoded
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with 15 bits (because 18002 isn't a factor of 2 and doesn't fit in
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14 bits). So the file format maximum is 32767 selectors.
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Some bzip2 encoders might actually have written out more selectors
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than the theoretical maximum because they rounded up the number of
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selectors to some convenient factor of 8.
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The extra 14766 selectors can never be validly used by the decompression
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algorithm. So we can read them, but then discard them.
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This is effectively what was done (by accident) before we added a
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check for nSelectors to be at most BZ_MAX_SELECTORS to mitigate
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CVE-2019-12900.
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The extra selectors were written out after the array inside the
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EState struct. But the struct has extra space allocated after the
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selector arrays of 18060 bytes (which is larger than 14766).
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All of which will be initialized later (so the overwrite of that
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space with extra selector values would have been harmless).
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Note by jamartis:
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The original patch Described above also reverts some changes that were made after 1.0.6.
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Since these changes are not yet present in 1.0.6, they don't need to be reverted and are thus
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removed from the original patch
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---
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diff --git a/decompress.c b/decompress.c
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index 20ce493..3303499 100644
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--- a/decompress.c
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+++ b/decompress.c
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@@ -296,8 +296,14 @@ Int32 BZ2_decompress ( DState* s )
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j++;
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if (j >= nGroups) RETURN(BZ_DATA_ERROR);
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}
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- s->selectorMtf[i] = j;
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+ /* Having more than BZ_MAX_SELECTORS doesn't make much sense
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+ since they will never be used, but some implementations might
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+ "round up" the number of selectors, so just ignore those. */
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+ if (i < BZ_MAX_SELECTORS)
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+ s->selectorMtf[i] = j;
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}
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+ if (nSelectors > BZ_MAX_SELECTORS)
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+ nSelectors = BZ_MAX_SELECTORS;
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/*--- Undo the MTF values for the selectors. ---*/
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{
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--
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cgit
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