Bug found in Ext2Fsd 0.60

Dear all,

We just found a bug in Ext2Fsd 0.60 during code inspection: For extent-based files
that have unwritten extents, writing attempts might cause silent data corruption of
other files or the whole file system. Thought the possibility of data corruption is very
small, to keep your data safe, better not writing any data to EXT4 volumes.

We’ve removed Ext2Fsd 0.60 packages from SourceForge. Right now we are working
on resolving this issue. Likely we will release version 0.61 this weekend.

Matt Wu

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22 Responses to “Bug found in Ext2Fsd 0.60”

  1. SandPox Says:

    Did you know what kind of file when write can caused data corruption? like big size, small size, file name contain unicode…?

    [Reply]

    ngkaho Reply:

    Files that are generated through fallocate

    [Reply]

  2. Urusai Says:

    I install my steam games on ext4 partition. With 0.60 when i verify my game cache, it found all game files faulty. Is this somehow connected to that?

    [Reply]

    ngkaho Reply:

    No idea… Are you checking your game cache on Windows?

    [Reply]

    ngkaho Reply:

    You may make checksums for your game cache on Linux, then make another checksums on Windows to see whether there is difference or not. I have no idea whether Steam use fallocate() or not.

    [Reply]

    Urusai Reply:

    Yeah i’m checking game cache on windows. I’ll try your suggestion, thanks. Went back to 0.53 and the problem seems to be gone.

    [Reply]

    Matt Reply:

    The possible reason is: 0.60 doesn’t correctly handle unwritten holes thus the holes will be filled by garbage data in disk.

    0.61 does handle the clearance of garbage holes to make sure data consistency. Give it a try please !

    [Reply]

    Urusai Reply:

    Just tried it and same issue.

    [Reply]

    Urusai Reply:

    Checksum works though.

    [Reply]

    ngkaho Reply:

    Maybe because Steam on Windows cannot identify game files downloaded by Steam on Linux?(That makes sence because the executable downloaded by Steam on Linux is ELF but not PE.

    [Reply]

    ngkaho Reply:

    ok, i can reproduce the same problem there.

    [Reply]

    ngkaho Reply:

    And the file checksums are correct.

    [Reply]

    ngkaho Reply:

    But they just failed to pass Steam validation

    [Reply]

    Matt Reply:

    This issue should be fixed in v0.62. Please have a try to verify:
    http://sourceforge.net/projects/ext2fsd/files/Ext2fsd/0.62/

    The root reason of validation failure is: Ext2Fsd direct i/o reports wrong read-length (longer than actual file size), then the checksum programs would do calculation of these extra data, thus it leads to verification failures.

    [Reply]

    Urusai Reply:

    Sorry, I was busy couldn’t reply. I just tried 0.62 and problem is gone! Thank you for your hard work 🙂

    [Reply]

    Matt Reply:

    That’s great. Thanks 🙂

    [Reply]

  3. Matt Says:

    Hey guys,

    How much longer until Ext2Fsd 0.61 is available?

    Thanks in advance

    [Reply]

    Matt Reply:

    0.61 was just released! Not long at all 🙂

    [Reply]

    Matt Reply:

    So was 0.62. Then what about 0.63 ?! Haha

    [Reply]

  4. Alberto Says:

    Looking forward the new version, since I didn’t get the 0.60 and I use quite a lot Ext4.

    [Reply]

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