linux-ext4 - [Bug 218648] New: ext4: previously opened file remains writeable on readonly ext4 filesystem; Data loss.

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

https://bugzilla.kernel.org/show_bug.cgi?id=218648

            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@...nel-bugs.osdl.org
          Reporter: zsolt@...egrity.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 filesystem. 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 readonly
ext4. Of course, this changes will be lost on reboot.

So the readonly filesystem blocked the new open for writing, but the prevously
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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