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From 1c127eb3cb7653bd61b61f9c3cfeb36fd10edab1 Mon Sep 17 00:00:00 2001
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From: Even Rouault <even.rouault@spatialys.com>
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Date: Sat, 12 May 2018 15:32:31 +0200
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Subject: [PATCH 3/4] LZWDecodeCompat(): fix potential index-out-of-bounds
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write. Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2780 /
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CVE-2018-8905
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The fix consists in using the similar code LZWDecode() to validate we
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don't write outside of the output buffer.
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---
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libtiff/tif_lzw.c | 18 ++++++++++++------
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1 file changed, 12 insertions(+), 6 deletions(-)
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diff --git a/libtiff/tif_lzw.c b/libtiff/tif_lzw.c
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index bc8f9c8..186ea3c 100644
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--- a/libtiff/tif_lzw.c
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+++ b/libtiff/tif_lzw.c
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@@ -604,6 +604,7 @@ LZWDecodeCompat(TIFF* tif, uint8* op0, tmsize_t occ0, uint16 s)
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char *tp;
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unsigned char *bp;
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int code, nbits;
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+ int len;
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long nextbits, nextdata, nbitsmask;
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code_t *codep, *free_entp, *maxcodep, *oldcodep;
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@@ -755,13 +756,18 @@ LZWDecodeCompat(TIFF* tif, uint8* op0, tmsize_t occ0, uint16 s)
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} while (--occ);
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break;
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}
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- assert(occ >= codep->length);
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- op += codep->length;
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- occ -= codep->length;
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- tp = op;
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+ len = codep->length;
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+ tp = op + len;
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do {
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- *--tp = codep->value;
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- } while( (codep = codep->next) != NULL );
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+ int t;
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+ --tp;
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+ t = codep->value;
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+ codep = codep->next;
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+ *tp = (char)t;
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+ } while (codep && tp > op);
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+ assert(occ >= len);
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+ op += len;
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+ occ -= len;
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} else {
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*op++ = (char)code;
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occ--;
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--
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2.17.0
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