linux-kernel - Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem

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Date:   Mon, 22 May 2023 20:36:23 +0800
From:   Heming Zhao <heming.zhao@...e.com>
To:     Luís Henriques <lhenriques@...e.de>
Cc:     Joseph Qi <joseph.qi@...ux.alibaba.com>,
        ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>
Subject: Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only
 filesystem

On Mon, May 22, 2023 at 01:23:07PM +0100, Luís Henriques wrote:
> Joseph Qi <joseph.qi@...ux.alibaba.com> writes:
> 
> > On 5/22/23 6:25 PM, Luís Henriques wrote:
> >> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
> >> fstest generic/452.  After mounting a filesystem as read-only, quotas are
> >
> > generic/452 is for testing ext4 mounted with dax and ro.
> > But ocfs2 doesn't support dax yet.
> 
> Right, but I think it's still useful to run the 'generic' test-suite in a
> filesystem.  We can always find issues in the test itself or, in this
> case, a bug in the filesystem.

It looks you did some special steps for 452. In my env, without changing
anything, I could pass this case successfully. 

- Heming

> 
> >> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
> >> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
> >> crash.
> >
> > In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
> > Do you mean remount as readonly?
> 
> Yes, sorry. Instead of "mounting", the patch changelog should say
> 
>   "After remounting a filesystem as read-only..."
> 
> Cheers,
> -- 
> Luís
> 
> >
> > Thanks,
> > Joseph
> >
> >> 
> >> Cc: <stable@...r.kernel.org>
> >> Signed-off-by: Luís Henriques <lhenriques@...e.de>
> >> ---
> >>  fs/ocfs2/super.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >> 
> >> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> >> index 0b0e6a132101..988d1c076861 100644
> >> --- a/fs/ocfs2/super.c
> >> +++ b/fs/ocfs2/super.c
> >> @@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
> >>  	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
> >>  		if (!sb_has_quota_loaded(sb, type))
> >>  			continue;
> >> -		oinfo = sb_dqinfo(sb, type)->dqi_priv;
> >> -		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> >> +		if (!sb_has_quota_suspended(sb, type)) {
> >> +			oinfo = sb_dqinfo(sb, type)->dqi_priv;
> >> +			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> >> +		}
> >>  		inode = igrab(sb->s_dquot.files[type]);
> >>  		/* Turn off quotas. This will remove all dquot structures from
> >>  		 * memory and so they will be automatically synced to global
>