linux-kernel - Re: [PATCH 00/17] fs, btrfs refcount conversions

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Message-ID: <20170309160234.GH14605@twin.jikos.cz>
Date:   Thu, 9 Mar 2017 17:02:34 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-btrfs@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, jbacik@...com, clm@...com,
        dsterba@...e.com
Subject: Re: [PATCH 00/17] fs, btrfs refcount conversions

On Fri, Mar 03, 2017 at 10:55:09AM +0200, Elena Reshetova wrote:
> Now when new refcount_t type and API are finally merged
> (see include/linux/refcount.h), the following
> patches convert various refcounters in the btrfs filesystem from atomic_t
> to refcount_t. By doing this we prevent intentional or accidental
> underflows or overflows that can led to use-after-free vulnerabilities.
> 
> The below patches are fully independent and can be cherry-picked separately.
> Since we convert all kernel subsystems in the same fashion, resulting
> in about 300 patches, we have to group them for sending at least in some
> fashion to be manageable. Please excuse the long cc list.

Thanks, the patchset looks good to me, I'm going to add it to the 4.12 queue.

> These patches have been tested with xfstests by running btrfs-related tests.
> btrfs debug was enabled, warns on refcount errors, too. No output related to
> refcount errors produced. However, the following errors were during the run:
>  * tests btrfs/078, btrfs/114, btrfs/115, no errors anywhere in dmesg, but
>  process hangs. They all seem to be around qgroup, sometimes error visible
>  such as qgroup scan failed -4 before it blocks, but not always.
>  * test btrfs/104 dmesg has additional error output:
>  BTRFS warning (device vdc): qgroup 258 reserved space underflow, have: 0,
>  to free: 4096
>  I tried looking at the code on what causes the failure, but could not figure
>  it out. It doesn't seem to be related to any refcount changes at least IMO.
> 
> The above test failures are hard for me to understand and interpreted, but
> they don't seem to relate to refcount conversions.

I don't think they're related to the refcount updates so we'll address
them.