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Date:   Thu, 17 Sep 2020 16:45:29 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Bob Peterson <rpeterso@redhat.com>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Sasha Levin <sashal@kernel.org>,
        Daniel Craig <Daniel.Craig@csiro.au>,
        Nicolas Courtel <courtel@cena.fr>,
        Salvatore Bonaccorso <carnil@debian.org>
Subject: Re: [PATCH 4.19 142/206] gfs2: fix use-after-free on transaction ail
 lists
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On Tue, Sep 15, 2020 at 12:52:01PM -0400, Bob Peterson wrote:
> ----- Original Message -----
> > Hi Bob, hi Greg,
> > 
> > On Fri, Sep 11, 2020 at 08:49:14AM -0400, Bob Peterson wrote:
> > > ----- Original Message -----
> > > > On Fri, Sep 11, 2020 at 08:08:35AM -0400, Bob Peterson wrote:
> > > > > ----- Original Message -----
> > > > > > On Thu, Sep 10, 2020 at 09:43:19PM +0200, Salvatore Bonaccorso wrote:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > On Tue, Jun 23, 2020 at 09:57:50PM +0200, Greg Kroah-Hartman wrote:
> > > > > > > > From: Bob Peterson <rpeterso@redhat.com>
> > > > > > > > 
> > > > > > > > [ Upstream commit 83d060ca8d90fa1e3feac227f995c013100862d3 ]
> > > > > > > > 
> > > > > > > > Before this patch, transactions could be merged into the system
> > > > > > > > transaction by function gfs2_merge_trans(), but the transaction
> > > > > > > > ail
> > > > > > > > lists were never merged. Because the ail flushing mechanism can
> > > > > > > > run
> > > > > > > > separately, bd elements can be attached to the transaction's
> > > > > > > > buffer
> > > > > > > > list during the transaction (trans_add_meta, etc) but quickly
> > > > > > > > moved
> > > > > > > > to its ail lists. Later, in function gfs2_trans_end, the
> > > > > > > > transaction
> > > > > > > > can be freed (by gfs2_trans_end) while it still has bd elements
> > > > > > > > queued to its ail lists, which can cause it to either lose track
> > > > > > > > of
> > > > > > > > the bd elements altogether (memory leak) or worse, reference the
> > > > > > > > bd
> > > > > > > > elements after the parent transaction has been freed.
> > > > > > > > 
> > > > > > > > Although I've not seen any serious consequences, the problem
> > > > > > > > becomes
> > > > > > > > apparent with the previous patch's addition of:
> > > > > > > > 
> > > > > > > > 	gfs2_assert_warn(sdp, list_empty(&tr->tr_ail1_list));
> > > > > > > > 
> > > > > > > > to function gfs2_trans_free().
> > > > > > > > 
> > > > > > > > This patch adds logic into gfs2_merge_trans() to move the merged
> > > > > > > > transaction's ail lists to the sdp transaction. This prevents the
> > > > > > > > use-after-free. To do this properly, we need to hold the ail
> > > > > > > > lock,
> > > > > > > > so we pass sdp into the function instead of the transaction
> > > > > > > > itself.
> > > > > > > > 
> > > > > > > > Signed-off-by: Bob Peterson <rpeterso@redhat.com>
> > > > > > > > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> > > > > > > > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > > > > (snip)
> > > > > > > 
> > > > > > > In Debian two user confirmed issues on writing on a GFS2 partition
> > > > > > > with this commit applied. The initial Debian report is at
> > > > > > > https://bugs.debian.org/968567 and Daniel Craig reported it into
> > > > > > > Bugzilla at https://bugzilla.kernel.org/show_bug.cgi?id=209217 .
> > > > > > > 
> > > > > > > Writing to a gfs2 filesystem fails and results in a soft lookup of
> > > > > > > the
> > > > > > > machine for kernels with that commit applied. I cannot reporduce
> > > > > > > the
> > > > > > > issue myself due not having a respective setup available, but
> > > > > > > Daniel
> > > > > > > described a minimal serieos of steps to reproduce the issue.
> > > > > > > 
> > > > > > > This might affect as well other stable series where this commit was
> > > > > > > applied, as there was a similar report for someone running 5.4.58
> > > > > > > in
> > > > > > > https://www.redhat.com/archives/linux-cluster/2020-August/msg00000.html
> > > > > > 
> > > > > > Can you report this to the gfs2 developers?
> > > > > > 
> > > > > > thanks,
> > > > > > 
> > > > > > greg k-h
> > > > > 
> > > > > Hi Greg,
> > > > > 
> > > > > No need. The patch came from the gfs2 developers. I think he just wants
> > > > > it added to a stable release.
> > > > 
> > > > What commit needs to be added to a stable release?
> > > > 
> > > > confused,
> > > > 
> > > > greg k-h
> > > 
> > > Sorry Greg,
> > > 
> > > It's pretty early here and the caffeine hadn't quite hit my system.
> > > The problem is most likely that 4.19.132 is missing this upstream patch:
> > > 
> > > cbcc89b630447ec7836aa2b9242d9bb1725f5a61
> > > 
> > > I'm not sure how or why 83d060ca8d90fa1e3feac227f995c013100862d3 got
> > > put into stable without a stable CC but cbcc89b6304 is definitely
> > > required.
> > > 
> > > I'd like to suggest Salvatore try cherry-picking this patch to see if
> > > it fixes the problem, and if so, perhaps Greg can add it to stable.
> > 
> > I can confirm (Daniel was able to test): Applying cbcc89b63044 ("gfs2:
> > initialize transaction tr_ailX_lists earlier") fixes the issue. So
> > would be great if you can pick that up for stable for those series
> > which had 83d060ca8d90 ("gfs2: fix use-after-free on transaction ail
> > lists") as well.
> > 
> > Regards,
> > Salvatore
> > 
> > 
> 
> Hi Greg,
> 
> As per Salvatore's email above, can you please cherry-pick GFS2 patch
> cbcc89b630447ec7836aa2b9242d9bb1725f5a61 to the stable releases like
> 4.19 to which ("gfs2: fix use-after-free on transaction ail lists")
> (83d060ca8d90fa1e3feac227f995c013100862d3) was applied? Thanks.

Now queued up, thanks.

greg k-h