Re: [PATCH] fs: erofs: remember if kobject_init_and_add was done

From: Gao Xiang <hsiangkao@linux.alibaba.com>
To: Huang Jianan <jnhuang95@gmail.com>
Cc: Dongliang Mu <dzm91@hust.edu.cn>, Gao Xiang <xiang@kernel.org>,
	Chao Yu <chao@kernel.org>, syzkaller <syzkaller@googlegroups.com>,
	linux-erofs@lists.ozlabs.org,
	Dongliang Mu <mudongliangabcd@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs: erofs: remember if kobject_init_and_add was done
Date: Tue, 15 Mar 2022 18:55:50 +0800	[thread overview]
Message-ID: <YjBwtqsEOZ5JbqvS@B-P7TQMD6M-0146.local> (raw)
In-Reply-To: <bca8f865-bc3e-44d7-7298-c2c7e8973580@gmail.com>

On Tue, Mar 15, 2022 at 06:43:01PM +0800, Huang Jianan wrote:
> 在 2022/3/15 15:51, Dongliang Mu 写道:
> > From: Dongliang Mu <mudongliangabcd@gmail.com>
> > 
> > Syzkaller hit 'WARNING: kobject bug in erofs_unregister_sysfs'. This bug
> > is triggered by injecting fault in kobject_init_and_add of
> > erofs_unregister_sysfs.
> > 
> > Fix this by remembering if kobject_init_and_add is successful.
> > 
> > Note that I've tested the patch and the crash does not occur any more.
> > 
> > Reported-by: syzkaller <syzkaller@googlegroups.com>
> > Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
> > ---
> >   fs/erofs/internal.h | 1 +
> >   fs/erofs/sysfs.c    | 9 ++++++---
> >   2 files changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> > index 5aa2cf2c2f80..9e20665e3f68 100644
> > --- a/fs/erofs/internal.h
> > +++ b/fs/erofs/internal.h
> > @@ -144,6 +144,7 @@ struct erofs_sb_info {
> >   	u32 feature_incompat;
> >   	/* sysfs support */
> > +	bool s_sysfs_inited;
> 
> Hi Dongliang,
> 
> How about using sbi->s_kobj.state_in_sysfs to avoid adding a extra member in
> sbi ?

Ok, I have no tendency of these (I'm fine with either ways).
I've seen some usage like:

static inline int device_is_registered(struct device *dev)
{
        return dev->kobj.state_in_sysfs;
}

But I'm still not sure if we need to rely on such internal
interface.. More thoughts?

Thanks,
Gao Xiang

> 
> Thanks,
> Jianan
> 
> >   	struct kobject s_kobj;		/* /sys/fs/erofs/<devname> */
> >   	struct completion s_kobj_unregister;
> >   };
> > diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
> > index dac252bc9228..2b48a4df19b4 100644
> > --- a/fs/erofs/sysfs.c
> > +++ b/fs/erofs/sysfs.c
> > @@ -209,6 +209,7 @@ int erofs_register_sysfs(struct super_block *sb)
> >   				   "%s", sb->s_id);
> >   	if (err)
> >   		goto put_sb_kobj;
> > +	sbi->s_sysfs_inited = true;
> >   	return 0;
> >   put_sb_kobj:
> > @@ -221,9 +222,11 @@ void erofs_unregister_sysfs(struct super_block *sb)
> >   {
> >   	struct erofs_sb_info *sbi = EROFS_SB(sb);
> > -	kobject_del(&sbi->s_kobj);
> > -	kobject_put(&sbi->s_kobj);
> > -	wait_for_completion(&sbi->s_kobj_unregister);
> > +	if (sbi->s_sysfs_inited) {
> > +		kobject_del(&sbi->s_kobj);
> > +		kobject_put(&sbi->s_kobj);
> > +		wait_for_completion(&sbi->s_kobj_unregister);
> > +	}
> >   }
> >   int __init erofs_init_sysfs(void)