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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Jan 30, 2019 at 08:11:17PM +0900, 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
> 

Obviously debugfs_lookup() should have its return value checked, so
that's fine :)

But how are we getting an error with dput()?  Are you sure this is a
debugfs issue and not a relayfs problem?

I'll send patches to clean up the tracing code's use of debugfs later,
as it is, I don't see anything obviously wrong with it.

thanks,

greg k-h