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

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Message-ID: <27008e5f-9dfc-a09a-cdb9-824d470fb9dd@I-love.SAKURA.ne.jp>
Date:   Wed, 30 Jan 2019 20:26:24 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Omar Sandoval <osandov@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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 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").