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From 58a898cb4459055bb488ca815c23b880c242a27d Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Sat, 12 May 2018 15:32:31 +0200
Subject: [PATCH] LZWDecodeCompat(): fix potential index-out-of-bounds write. Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2780 / CVE-2018-8905
The fix consists in using the similar code LZWDecode() to validate we
don't write outside of the output buffer.
---
libtiff/tif_lzw.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/libtiff/tif_lzw.c b/libtiff/tif_lzw.c
index 4ccb443..94d85e3 100644
--- a/libtiff/tif_lzw.c
+++ b/libtiff/tif_lzw.c
@@ -602,6 +602,7 @@ LZWDecodeCompat(TIFF* tif, uint8* op0, tmsize_t occ0, uint16 s)
char *tp;
unsigned char *bp;
int code, nbits;
+ int len;
long nextbits, nextdata, nbitsmask;
code_t *codep, *free_entp, *maxcodep, *oldcodep;
@@ -753,13 +754,18 @@ LZWDecodeCompat(TIFF* tif, uint8* op0, tmsize_t occ0, uint16 s)
} while (--occ);
break;
}
- assert(occ >= codep->length);
- op += codep->length;
- occ -= codep->length;
- tp = op;
+ len = codep->length;
+ tp = op + len;
do {
- *--tp = codep->value;
- } while( (codep = codep->next) != NULL );
+ int t;
+ --tp;
+ t = codep->value;
+ codep = codep->next;
+ *tp = (char)t;
+ } while (codep && tp > op);
+ assert(occ >= len);
+ op += len;
+ occ -= len;
} else {
*op++ = (char)code;
occ--;
--
libgit2 0.27.0
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