linux-ext4 - [Bug 219300] ext4 corrupts data on a specific pendrive

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Message-ID: <bug-219300-13602-Tor3Eyz3zS@https.bugzilla.kernel.org/>
Date: Mon, 23 Sep 2024 06:26:35 +0000
From: bugzilla-daemon@...nel.org
To: linux-ext4@...r.kernel.org
Subject: [Bug 219300] ext4 corrupts data on a specific pendrive

https://bugzilla.kernel.org/show_bug.cgi?id=219300

Theodore Tso (tytso@....edu) changed:

           What    |Removed                     |Added
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                 CC|                            |tytso@....edu

--- Comment #5 from Theodore Tso (tytso@....edu) ---
Ext4 uses a block allocation algorithm which spreads the blocks used by files
across the entire storage device in order to reduce file fragmentation.   There
are cheap thumb drives that claim to be, say, 16GB, but which only have 8GB of
flash, and they rely on the fact that some Windows file systems (FAT and NTFS)
allocates blocks starting at the low-numbered block numbers, and so if there is
a fake/scammy USB thumb drive (the kind that you buy in the back alley of
Shenzhen, or at a deap discount in the checkout line of Microcenter, or a
really dodgy vendor on Amazon Marketplace at a price which is too good to be
true), it might work on Windows so long as you don't actually try to store that
many files on it.

In any case, the console messages are very clearly I/O errors and the LBA
sector number reported is a high-numbered address: 60278752.    Whether this is
just a failed thumbdrive, or one which is deliberately sold as a fake is
unclear, but I would suggest trying to read and write to all of the sectors of
the disk.   Fundamentally, ext4 assumes that the storage device is valid; and
if it is not valid (e.g., has I/O errors when you try to read or write to
portions of the disk), that's the storage device's problem, not ext4.

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