linux-kernel - Re: Fw:Re: [PATCH] fs: nilfs2: fix memory leak in nilfs sysfs create device group

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Date:   Tue, 15 Mar 2022 13:49:39 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Ryusuke Konishi <konishi.ryusuke@...il.com>
Cc:     Pavel Skripkin <paskripkin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-nilfs <linux-nilfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nanyong Sun <sunnanyong@...wei.com>,
        慕冬亮 <dzm91@...t.edu.cn>
Subject: Re: Fw:Re: [PATCH] fs: nilfs2: fix memory leak in nilfs sysfs create
 device group

On Tue, Mar 15, 2022 at 12:46 PM Ryusuke Konishi
<konishi.ryusuke@...il.com> wrote:
>
> On Tue, Mar 15, 2022 at 10:59 AM Dongliang Mu <mudongliangabcd@...il.com> wrote:
> >
> > On Sun, Mar 13, 2022 at 9:35 PM Dongliang Mu <mudongliangabcd@...il.com> wrote:
> > >
> > > On Sun, Mar 13, 2022 at 12:01 AM Ryusuke Konishi
> > > <konishi.ryusuke@...il.com> wrote:
> > > >
> > > > Hi Pavel and Dongliang,
> > > >
> > > > On Sun, Mar 13, 2022 at 12:16 AM Pavel Skripkin <paskripkin@...il.com> wrote:
> > > > >
> > > > > Hi Ryusuke,
> > > > >
> > > > > On 3/12/22 18:11, Ryusuke Konishi wrote:
> > > > > >> In case of nilfs_attach_log_writer() error code jumps to
> > > > > >> failed_checkpoint label and calls destroy_nilfs() which should call
> > > > > >> nilfs_sysfs_delete_device_group().
> > > > > >
> > > > > > nilfs_sysfs_delete_device_group() is called in destroy_nilfs()
> > > > > > if nilfs->ns_flags has THE_NILFS_INIT flag -- nilfs_init() inline
> > > > > > function tests this flag.
> > > > > >
> > > > > > The flag is set after init_nilfs() succeeded at the beginning of
> > > > > > nilfs_fill_super() because the set_nilfs_init() inline in init_nilfs() sets it.
> > > > > >
> > > > > > So,  nilfs_sysfs_delete_group() seems to be called in case of
> > > > > > the above failure.   Am I missing something?
> > > > > >
> > > > >
> > > > > Yeah, that's what I mean :) I can't see how reported issue is possible
> > > > > with current code.
> > > > >
> > > > >
> > > > > Sorry for not being clear
> > > >
> > > > Understood, thanks for the reply.
> > > >
> > > > If so,  the case where nilfs_sysfs_create_device_group() itself failed,
> > > > is suspicious as mentioned in the previous mail.   A possible scenario
> > > > I guess is :
> > > >
> > > > - nilfs_sysfs_create_device_group() on the first mount try fails and leaks
> > > >   due to lack of kobject_del() in the error path.
> > > > - Then, nilfs_sysfs_create_device_group() on the next mount try hits
> > > >   the leak detector at kobject_init_and_add().
> > > >
> > > > So, if the leak bug is reproducible, I'd like to ask Dongliang to
> > > > test the effect of the first patch.
> > >
> > > If my local syzkaller instance gets a reproducer, I will try to do this.
> > >
> > > >
> > > > Regards,
> > > > Ryusuke Konishi
> >
> > Hi Ryusuke,
> >
> > The crash still occurred in my newly set up syzkaller instance. It
> > appears after two days' fuzzing.
> >
> > I remember you suggested me to add kobject_del just for testing,
> > right? And let's see if this crash still occurs any more.
>
> You need a few days to reproduce it ?
> If so, I think this confirmation method is uncertain.
> In that case, I will try inserting an artificial error by changing
> nilfs_sysfs_create_device_group() a bit to confirm if the same crash occurs.

I am reproducing another bug [1] recently. If you can spare some time
figuring out the underlying issue, that's really great. Or we can wait
some time for the bug to disclose more, after all, it is only a rare
memory leak.

[1] https://syzkaller.appspot.com/bug?extid=045796dbe294d53147e6

>
> Ryusuke Konishi