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From: bugzilla-daemon@kernel.org
To: linux-ext4@vger.kernel.org
Subject: [Bug 218648] New: ext4: previously opened file remains writeable on
 readonly ext4 filesystem; Data loss.
Date: Wed, 27 Mar 2024 09:31:57 +0000
Message-ID: <bug-218648-13602@https.bugzilla.kernel.org/>
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https://bugzilla.kernel.org/show_bug.cgi?id=3D218648

            Bug ID: 218648
           Summary: ext4: previously opened file remains writeable on
                    readonly ext4 filesystem; Data loss.
           Product: File System
           Version: 2.5
    Kernel Version: 6.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: ext4
          Assignee: fs_ext4@kernel-bugs.osdl.org
          Reporter: zsolt@integrity.hu
        Regression: No

I have a VM on KVM. The KVM image is on GlusterFS and for the test I stopped
the gluster server. If this backend goes offline, the ext4 filesystem will =
be
readonly in the VM. It's OK.

But if I have a previously opened file (for writing) in this ext4 filesyste=
m. I
can continue to write. The "ls -l" command shows, the file is growing (but =
the
modification time isn't changes anymore).
Second test: previously mmap-ed file. I can rewrite the 4k blocks on readon=
ly
ext4. Of course, this changes will be lost on reboot.

So the readonly filesystem blocked the new open for writing, but the prevou=
sly
opened file can I write, but the data will be lost.

Are these cases normal on readonly filesystem or a bug?

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