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From 1e07c98dfcbd8ac10ee02088f08235f5e1700148 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Dan=20=C4=8Cerm=C3=A1k?= <dan.cermak@cgc-instruments.com>
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Date: Wed, 27 Sep 2017 23:38:49 +0200
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Subject: Fixed wrong brackets: size*count + pad can overflow before the cast
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=> Should fix #76 (most of the work has been done by Robin Mills in
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6e3855aed7ba8bb4731fc4087ca7f9078b2f3d97)
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The problem with #76 is the contents of the 26th IFD, with the
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following contents:
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tag: 0x8649
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type: 0x1
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count: 0xffff ffff
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offset: 0x4974
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The issue is the size of count (uint32_t), as adding anything to it
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causes an overflow. Especially the expression:
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(size*count + pad+20)
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results in an overflow and gives 20 as a result instead of
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0x100000014, thus the condition in the if in the next line is false
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and the program continues to run (until it crashes at io.read).
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To properly account for the overflow, the brackets have to be removed,
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as then the result is saved in the correctly sized type and not cast
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after being calculated in the smaller type.
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diff --git a/src/image.cpp b/src/image.cpp
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index ec5b873e..199671b9 100644
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--- a/src/image.cpp
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+++ b/src/image.cpp
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@@ -401,7 +401,7 @@ namespace Exiv2 {
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// if ( offset > io.size() ) offset = 0; // Denial of service?
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// #55 memory allocation crash test/data/POC8
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- long long allocate = (long long) (size*count + pad+20);
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+ long long allocate = (long long) size*count + pad+20;
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if ( allocate > (long long) io.size() ) {
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throw Error(57);
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}
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