Re: [PATCH 5.19 005/192] net: mvpp2: debugfs: fix memory leak when using debugfs_lookup()

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Tue, Sep 13, 2022 at 04:01:51PM +0200, Greg Kroah-Hartman wrote:
> From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> commit fe2c9c61f668cde28dac2b188028c5299cedcc1e upstream.
> 
> When calling debugfs_lookup() the result must have dput() called on it,
> otherwise the memory will leak over time.  Fix this up to be much
> simpler logic and only create the root debugfs directory once when the
> driver is first accessed.  That resolves the memory leak and makes
> things more obvious as to what the intent is.
> 
> Cc: Marcin Wojtas <mw@semihalf.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
> Cc: stable <stable@kernel.org>
> Fixes: 21da57a23125 ("net: mvpp2: add a debugfs interface for the Header Parser")
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c
> @@ -700,10 +700,10 @@ void mvpp2_dbgfs_cleanup(struct mvpp2 *p
>  
>  void mvpp2_dbgfs_init(struct mvpp2 *priv, const char *name)
>  {
> -	struct dentry *mvpp2_dir, *mvpp2_root;
> +	static struct dentry *mvpp2_root;
> +	struct dentry *mvpp2_dir;
>  	int ret, i;
>  
> -	mvpp2_root = debugfs_lookup(MVPP2_DRIVER_NAME, NULL);
>  	if (!mvpp2_root)
>  		mvpp2_root = debugfs_create_dir(MVPP2_DRIVER_NAME, NULL);

This looks broken to me.

What happens if this is built as a module, and the module is loaded,
binds (and creates the directory), then is removed, and then re-
inserted?  Nothing removes the old directory, so doesn't
debugfs_create_dir() fail, resulting in subsequent failure to add
any subsequent debugfs entries?

I don't think this patch should be backported to stable trees until
this point is addressed.

-- 
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