linux-ext4 - Re: [REPORT] kernel BUG at fs/ext4/inode.c:2620

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Message-ID: <YhcD0ugEyDMi4wXO@mit.edu>
Date:   Wed, 23 Feb 2022 23:04:34 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Lee Jones <lee.jones@...aro.org>, linux-ext4@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Dave Chinner <dchinner@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Bob Peterson <rpeterso@...hat.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Thumshirn <jth@...nel.org>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, cluster-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [REPORT] kernel BUG at fs/ext4/inode.c:2620 - page_buffers()

On Wed, Feb 23, 2022 at 04:44:07PM -0800, John Hubbard wrote:
> 
> Actually...I can confirm that real customers really are doing *exactly* 
> that! Despite the kernel crashes--because the crashes don't always 
> happen unless you have a large (supercomputer-sized) installation. And 
> even then it is not always root-caused properly.

Interesting.  The syzbot reproducer triggers *reliably* on ext4 using
a 2 CPU qemu kernel running on a laptop, and it doesn't require root,
so it's reasonable that Lee is pushing for a fix --- even if for the
Android O or newer, Seccomp can probably prohibit trap
process_vm_writev(2), but it seems unfortunate if say, someone running
a Docker container could take down the entire host OS.

  	 	   	      	       	      - Ted