linux-kernel - Re: [PATCH] dpaa2-mac: Fix potential null pointer dereference

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Date:   Sun, 27 Sep 2020 13:59:52 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Alex Dewar <alex.dewar90@...il.com>
CC:     Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dpaa2-mac: Fix potential null pointer dereference

On Sun, Sep 27, 2020 at 02:31:20PM +0100, Alex Dewar wrote:
> In dpaa2_pcs_destroy, variable pcs is dereference before it is
> null-checked. Fix this.
> 
> Addresses-Coverity: CID 1497159: Null pointer dereferences (REVERSE_INULL)
> Signed-off-by: Alex Dewar <alex.dewar90@...il.com>
> ---
>  drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> index 6ff64dd1cf27..09bf4fec1172 100644
> --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> @@ -291,11 +291,10 @@ static int dpaa2_pcs_create(struct dpaa2_mac *mac,
>  static void dpaa2_pcs_destroy(struct dpaa2_mac *mac)
>  {
>  	struct lynx_pcs *pcs = mac->pcs;
> -	struct device *dev = &pcs->mdio->dev;
>  
>  	if (pcs) {
>  		lynx_pcs_destroy(pcs);
> -		put_device(dev);
> +		put_device(&pcs->mdio->dev);
>  		mac->pcs = NULL;
>  	}
>  }

This would introduce another problem because you would access an already
freed pcs. Maybe just move the declaration and initialization of dev
inside the if statement.

Thanks, Ioana