linux-kernel - Re: BUG: unable to handle kernel paging request in dput (2)

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Date:   Wed, 30 Jan 2019 12:34:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Omar Sandoval <osandov@...com>,
        syzbot <syzbot+b382ba6a802a3d242790@...kaller.appspotmail.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...com>
Subject: Re: BUG: unable to handle kernel paging request in dput (2)

On Wed, Jan 30, 2019 at 08:26:24PM +0900, Tetsuo Handa wrote:
> On 2019/01/30 20:11, Tetsuo Handa wrote:
> > Hello, Omar.
> > 
> > syzbot is reporting a crash due to dput(-EINVAL) [1]. I think the location is
> > 
> >         dir = debugfs_lookup(buts->name, blk_debugfs_root);
> >         if (!dir)
> >                 bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);
> > 
> > added by commit 6ac93117ab009d39 ("blktrace: use existing disk debugfs directory").
> > 
> > Currently, Greg Kroah-Hartman is posting patches:
> > 
> >   When calling debugfs functions, there is no need to ever check the
> >   return value.  The function can work or not, but the code logic should
> >   never do something different based on this.
> > 
> > Omar, what do you want to do for this case?
> > 
> > [1] https://syzkaller.appspot.com/bug?extid=b382ba6a802a3d242790
> > 
> 
> The function which returned -EINVAL instead of NULL seems to be debugfs_lookup()
> modified by commit ff9fb72bc07705c0 ("debugfs: return error values, not NULL").

Ah, my fault then, yes, debugfs_lookup() should return NULL if nothing
is found.  My patch was wrong, let me go fix this up, thanks for the
report.

greg k-h