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RegionLoader: do not attempt to auto-repair chunks with oversized lengths

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In the old days, we used to try to correct this problem by adjusting the region header to match the
length found at the start of the chunk payload. However, this has a very good chance to cause corruption
of other chunks, since we can't do any fast overlap checks (an upsize might cause the chunk's alloocated
area to overlap into another one, causing corruption when either chunk's space gets written to).

This corruption risk has become more problematic since the
introduction of region garbage sector reuse, since a broken location
header could cause chunks to trash each others' saved data.

In addition, if there is a length mismatch, there's a good chance that the oversized chunk itself will
already be corrupted, so we'd just fail trying to decompress it later on.

So, instead of trying to fix this automatically, we bail and hope this doesn't occur often enough for
users to get upset, and allow external offline tools to attempt to repair the mess instead.
This commit is contained in:
Dylan K. Taylor 2020-12-27 18:50:52 +00:00
parent 873e8740e0
commit dea75a0687
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GPG Key ID: 8927471A91CAFD3D
1 changed files with 1 additions and 5 deletions
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6
src/pocketmine/level/format/io/region/RegionLoader.php
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@ -27,7 +27,6 @@ use pocketmine\level\format\ChunkException;
use pocketmine\level\format\io\exception\CorruptedChunkException;
use pocketmine\utils\AssumptionFailedError;
use pocketmine\utils\Binary;
use pocketmine\utils\MainLogger;
use function assert;
use function ceil;
use function chr;
@ -160,10 +159,7 @@ class RegionLoader{
}
if($length > ($this->locationTable[$index]->getSectorCount() << 12)){ //Invalid chunk, bigger than defined number of sectors
MainLogger::getLogger()->error("Chunk x=$x,z=$z length mismatch (expected " . ($this->locationTable[$index]->getSectorCount() << 12) . " sectors, got $length sectors)");
$old = $this->locationTable[$index];
$this->locationTable[$index] = new RegionLocationTableEntry($old->getFirstSector(), $length >> 12, time());
$this->writeLocationIndex($index);
throw new CorruptedChunkException("Chunk length mismatch (expected " . ($this->locationTable[$index]->getSectorCount() << 12) . " sectors, got $length sectors)");
}
$chunkData = fread($this->filePointer, $length);