linux-ext4 - [Bug 211971] Incorrect fix by e2fsck for blocks

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Message-ID: <bug-211971-13602-r6IDKRIC6B@https.bugzilla.kernel.org/>
Date:   Sat, 27 Feb 2021 00:58:36 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...r.kernel.org
Subject: [Bug 211971] Incorrect fix by e2fsck for blocks_count corruption

https://bugzilla.kernel.org/show_bug.cgi?id=211971

--- Comment #1 from Amy (enbyamy@...il.com) ---
Can you replicate this on modern 5.4 from kernel.org? -generic kernels
are from Canonical and are sometimes broken compared to upstream. If
you can't replicate this on mainline, you'll need to contact
Canonical. We can't do anything if the problem only persists on
distribution kernels.

On Fri, Feb 26, 2021 at 1:41 PM <bugzilla-daemon@...zilla.kernel.org> wrote:
>
> https://bugzilla.kernel.org/show_bug.cgi?id=211971
>
>             Bug ID: 211971
>            Summary: Incorrect fix by e2fsck for blocks_count corruption
>            Product: File System
>            Version: 2.5
>     Kernel Version: Linux 5.4.0-65-generic
>           Hardware: x86-64
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: ext4
>           Assignee: fs_ext4@...nel-bugs.osdl.org
>           Reporter: tmahmud@...tate.edu
>         Regression: No
>
> Created attachment 295497
>   --> https://bugzilla.kernel.org/attachment.cgi?id=295497&action=edit
> log files from mke2fs, dumpe2fs and e2fsck
>
> For an ext4 file system image with only one superblock, if the blocks_count
> field in superblock is corrupted, e2fsck fixed it incorrectly. In the fixed
> image, the corrupted blocks_count is unchanged and other fields (e.g., free
> blocks count) are changed accordingly.
> This issue also occurs in images with multiple superblocks too. For example,
> For an ext4 image with primary and backup superblock (backup superblocks are
> not located in default locations, e.g., it is located on 513rd block), if the
> blocks_count field in superblock is corrupted, e2fsck fixed it incorrectly.
> In
> the fixed image, the corrupted blocks_count is unchanged and other fields
> (e.g., free blocks count) are changed accordingly.
>
> e2fsprogs_version_used: e2fsprogs 1.45.6 (20-Mar-2020)
> The commands that I ran to recreate the scenario are:
> For image with only one superblock:
>
> dd if=/dev/zero bs=1024 count=8193 of=/home/hdd/image
> mke2fs -b 1024 image 8193
> debugfs -w image
> debugfs:  ssv blocks_count 4000
> debugfs:  q
> e2fsck -yf image
> e2fsck -yf image
>
> # e2fsck fixes the blocks_count corruption in correctly
> # In the clean image the blocks_count was 8193, in the fixed image the
> blocks_count is 4000
> #The second run of e2fsck is consistent with the first run, it doesn't fix
> anything, but blocks_count is still 4000
> # Expected that e2fsck would fix the blocks count corruption instead of
> changing other fields (e.g.,free blocks_count)
>
> For image with multiple superblocks:
> dd if=/dev/zero bs=1024 count=8193 of=/home/hdd/image1
> mke2fs -b 1024 -g 512 image1 8193
> debugfs -w image1
> debugfs:  ssv blocks_count 4000
> debugfs:  q
> e2fsck -yf image1
> e2fsck -yf image1
>
> # e2fsck fixes the blocks_count corruption in correctly
> # In the clean image the blocks_count was 8193, in the fixed image the
> blocks_count is 4000
> # The second run of e2fsck is consistent with the first run, it doesn't fix
> anything, but blocks_count is still 4000
> #There were 16 block groups in the clean image, but there are only 7 block
> groups in the fixed image
> # Expected that e2fsck would fix the blocks count corruption instead of
> changing other fields (e.g.,free blocks_count) and removing the block groups.
>
> I attached the images and also the logs from mke2fs, dumpe2fs and e2fsck.
>
> --
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