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Date:   Fri, 11 Sep 2020 08:08:35 -0400 (EDT)
From:   Bob Peterson <rpeterso@redhat.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Salvatore Bonaccorso <carnil@debian.org>,
        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>
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In-Reply-To: <20200911115816.GB3717176@kroah.com>
References: <20200623195316.864547658@linuxfoundation.org> <20200623195323.968867013@linuxfoundation.org> <20200910194319.GA131386@eldamar.local> <20200911115816.GB3717176@kroah.com>
Subject: Re: [PATCH 4.19 142/206] gfs2: fix use-after-free on transaction
 ail lists
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Thread-Topic: gfs2: fix use-after-free on transaction ail lists
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----- 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.

Regards,

Bob Peterson
GFS2 File System