File CVE-2020-18831.patch of Package exiv2.30966

From 20a13f00e2db24c58ee326e4c89a56469718b30e Mon Sep 17 00:00:00 2001
From: Kevin Backhouse <kev@semmle.com>
Date: Thu, 16 May 2019 13:22:53 +0100
Subject: [PATCH] Add better bounds checking in PngImage::printStructure().

---
 src/pngimage.cpp                        |  13 +++++++---

Index: exiv2-0.26/src/pngimage.cpp
===================================================================
--- exiv2-0.26.orig/src/pngimage.cpp
+++ exiv2-0.26/src/pngimage.cpp
@@ -251,7 +251,7 @@ namespace Exiv2 {
                 if (bufRead != cheaderBuf.size_) throw Error(20);
 
                 // Decode chunk data length.
-                uint32_t dataOffset = Exiv2::getULong(cheaderBuf.pData_, Exiv2::bigEndian);
+                const uint32_t dataOffset = Exiv2::getULong(cheaderBuf.pData_, Exiv2::bigEndian);
                 for (int i = 4; i < 8; i++) {
                     chType[i-4]=cheaderBuf.pData_[i];
                 }
@@ -266,7 +266,8 @@ namespace Exiv2 {
                 }
 
                 DataBuf   buff(dataOffset);
-                io_->read(buff.pData_,dataOffset);
+                bufRead = io_->read(buff.pData_,dataOffset);
+                enforce(bufRead == static_cast<long>(dataOffset), kerFailedToReadImageData);
                 io_->seek(restore, BasicIo::beg);
 
                 // format output
@@ -279,7 +280,8 @@ namespace Exiv2 {
                 if ( bPrint ) {
                     io_->seek(dataOffset, BasicIo::cur);// jump to checksum
                     byte checksum[4];
-                    io_->read(checksum,4);
+                    bufRead = io_->read(checksum,4);
+                    enforce(bufRead == 4, kerFailedToReadImageData);
                     io_->seek(restore, BasicIo::beg)   ;// restore file pointer
 
                     out << Internal::stringFormat("%8d | %-5s |%8d | "
@@ -310,9 +312,12 @@ namespace Exiv2 {
                     DataBuf   dataBuf;
                     byte*     data   = new byte[dataOffset+1];
                     data[dataOffset] = 0;
-                    io_->read(data,dataOffset);
+                    bufRead = io_->read(data,dataOffset);
+                    enforce(bufRead == static_cast<long>(dataOffset), kerFailedToReadImageData);
                     io_->seek(restore, BasicIo::beg);
                     uint32_t  name_l = (uint32_t) std::strlen((const char*)data)+1; // leading string length
+                    enforce(name_l <= dataOffset, kerCorruptedMetadata);
+
                     uint32_t  start  = name_l;
                     bool      bLF    = false;