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

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Message-ID: <a57047d6-8f57-3dde-f15f-b24f63d675cd@linux.alibaba.com>
Date:   Mon, 22 May 2023 20:01:25 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Luís Henriques <lhenriques@...e.de>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        Heming Zhao <heming.zhao@...e.com>
Subject: Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only
 filesystem



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. 

> 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?

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