From: Jan Kara <jack@suse.cz>
To: Zhang Yi <yi.zhang@huawei.com>
Cc: Jan Kara <jack@suse.cz>, "Theodore Y. Ts'o" <tytso@mit.edu>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
yangerkun <yangerkun@huawei.com>,
linfeilong@huawei.com
Subject: Re: [BUG && Question] question of SB_ACTIVE flag in ext4_orphan_cleanup()
Date: Tue, 30 Mar 2021 17:02:29 +0200 [thread overview]
Message-ID: <20210330150229.GC30749@quack2.suse.cz> (raw)
In-Reply-To: <b1a05885-1d7b-b9d1-80da-785633cbfc6a@huawei.com>
On Mon 29-03-21 17:20:35, Zhang Yi wrote:
> On 2021/3/23 1:25, Jan Kara wrote:
> > Hi!
> >
> > On Mon 22-03-21 23:24:23, Zhang Yi wrote:
> >> We find a use after free problem when CONFIG_QUOTA is enabled, the detail of
> >> this problem is below.
> >>
> >> mount_bdev()
> >> ext4_fill_super()
> >> sb->s_root = d_make_root(root);
> >> ext4_orphan_cleanup()
> >> sb->s_flags |= SB_ACTIVE; <--- 1. mark sb active
> >> ext4_orphan_get()
> >> ext4_truncate()
> >> ext4_block_truncate_page()
> >> mark_buffer_dirty <--- 2. dirty inode
> >> iput()
> >> iput_final <--- 3. put into lru list
> >> ext4_mark_recovery_complete <--- 4. failed and return error
> >> sb->s_root = NULL;
> >> deactivate_locked_super()
> >> kill_block_super()
> >> generic_shutdown_super()
> >> <--- 5. did not evict_inodes
> >> put_super()
> >> __put_super()
> >> <--- 6. put super block
> >>
> >> Because of the truncated inodes was dirty and will write them back later, it
> >> will trigger use after free problem. Now the question is why we need to set
> >> SB_ACTIVE bit when enable CONFIG_QUOTA below?
> >>
> >> #ifdef CONFIG_QUOTA
> >> /* Needed for iput() to work correctly and not trash data */
> >> sb->s_flags |= SB_ACTIVE;
> >>
> >> This code was merged long long ago in v2.6.6, IIUC, it may not affect
> >> the quota statistics it we evict inode directly in the last iput.
> >> In order to slove this UAF problem, I'm not sure is there any side effect
> >> if we just remove this code, or remove SB_ACTIVE and call evict_inodes()
> >> in the error path of ext4_fill_super().
> >>
> >> Could you give some suggestions?
> >
> > That's a very good question. I do remember that I've added this code back
> > then because otherwise orphan cleanup was loosing updates to quota files.
> > But you're right that now I don't see how that could be happening and it
> > would be nice if we could get rid of this hack (and even better if it also
> > fixes the problem you've found). I guess I'll just try and test this change
> > with various quota configurations to see whether something still breaks or
> > not. Thanks report!
> >
>
> Thanks for taking time to look at this, is this change OK under your various
> quota test cases?
Yes, I did tests both with journalled quotas and with ext4 quota feature
and the quota accounting was correct after orphan recovery. So just
removing the SB_ACTIVE setting is fine AFAICT. Will you send a patch or
should I do it?
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2021-03-30 15:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 15:24 [BUG && Question] question of SB_ACTIVE flag in ext4_orphan_cleanup() Zhang Yi
2021-03-22 17:25 ` Jan Kara
2021-03-29 9:20 ` Zhang Yi
2021-03-30 15:02 ` Jan Kara [this message]
2021-03-31 3:11 ` Zhang Yi
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