Re: [PATCH] rpc: properly check debugfs dentry before using it

["Schumaker, Anna" <Anna.Schumaker@netapp.com>]

On Tue, 2019-02-12 at 19:27 +0100, Greg Kroah-Hartman wrote:
> debugfs can now report an error code if something went wrong instead of
> just NULL.  So if the return value is to be used as a "real" dentry, it
> needs to be checked if it is an error before dereferencing it.
> 
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL"), but why debugfs files are not being created properly
> is an older issue, probably one that has always been there and should
> probably be looked at...
> 
> Cc: "J. Bruce Fields" <bfields@fieldses.org>
> Cc: Jeff Layton <jlayton@kernel.org>
> Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
> Cc: Anna Schumaker <anna.schumaker@netapp.com>
> Cc: linux-nfs@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Reported-by: David Howells <dhowells@redhat.com>
> Tested-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> ---
>  net/sunrpc/debugfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> I can take this through my tree if people don't object, or it can go
> through the NFS tree.  It does need to get merged before 5.0-final
> though.

I'm planning another bugfixes pull for 5.0, so I can take this patch and send it
with the others this week.

Thanks!
Anna

> 
> I also have a "larger" debugfs cleanup patch for this file, but that's
> not really 5.0-final material and I will send it out later.
> 
> thanks,
> 
> greg k-h
> 
> diff --git a/net/sunrpc/debugfs.c b/net/sunrpc/debugfs.c
> index 45a033329cd4..19bb356230ed 100644
> --- a/net/sunrpc/debugfs.c
> +++ b/net/sunrpc/debugfs.c
> @@ -146,7 +146,7 @@ rpc_clnt_debugfs_register(struct rpc_clnt *clnt)
>         rcu_read_lock();
>         xprt = rcu_dereference(clnt->cl_xprt);
>         /* no "debugfs" dentry? Don't bother with the symlink. */
> -       if (!xprt->debugfs) {
> +       if (IS_ERR_OR_NULL(xprt->debugfs)) {
>                 rcu_read_unlock();
>                 return;
>         }