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Date:   Wed, 10 Jun 2020 18:41:52 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Alexey Gladkov <gladkov.alexey@gmail.com>,
        syzbot <syzbot+4abac52934a48af5ff19@syzkaller.appspotmail.com>,
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Subject: Re: [PATCH] proc: s_fs_info may be NULL when proc_kill_sb is called
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On Wed, Jun 10, 2020 at 12:12:54PM -0500, Eric W. Biederman wrote:

> >  {
> >  	struct proc_fs_info *fs_info = proc_sb_info(sb);
> >  
> > -	if (fs_info->proc_self)
> > -		dput(fs_info->proc_self);
> > +	if (fs_info) {
> > +		if (fs_info->proc_self)
> > +			dput(fs_info->proc_self);
> >  
> > -	if (fs_info->proc_thread_self)
> > -		dput(fs_info->proc_thread_self);
> > +		if (fs_info->proc_thread_self)
> > +			dput(fs_info->proc_thread_self);
> > +
> > +		put_pid_ns(fs_info->pid_ns);
> > +		kfree(fs_info);

While we are at it, dput(NULL) is an explicit no-op.