Re: [PATCH] net: dsa: avoid null pointer dereference on p->phy

[Joe Perches]

On Sat, 2017-09-23 at 17:57 +0100, Colin King wrote:
> From: Colin Ian King <colin.k...@canonical.com>
> 
> Currently p->phy is being null checked in several places to avoid
> null pointer dereferences on p->phy, however, the final call
> to phy_attached_info on p->phy when p->phy will perform a null
> pointer dereference. Fix this by simply moving the call into
> the previous code block that is only executed if p->phy is
> not null.
> 
> Detected by CoverityScan, CID#1457034 ("Dereference after null check")
> 
> Fixes: 2220943a21e2 ("phy: Centralise print about attached phy")
> Signed-off-by: Colin Ian King <colin.k...@canonical.com>
> ---
>  net/dsa/slave.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 02ace7d462c4..29ab4e98639b 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -1115,10 +1115,9 @@ static int dsa_slave_phy_setup(struct net_device 
> *slave_dev)
>                               of_phy_deregister_fixed_link(port_dn);
>                       return ret;
>               }
> +             phy_attached_info(p->phy);
>       }
>  
> -     phy_attached_info(p->phy);
> -
>       return 0;
>  }

Huh?  Why move this into the test?

The test of the block above this change is

        if (!p->phy) {

Perhaps this should be
'
        if (p->phy)
                phy_attached_info(p->phy);

or simpler

        } else {
                phy_attached_info(p->phy);
        }

or maybe reverse the block

        if (p->phy) {
                phy_attached_info(p->phy);
        } else {
                ret = dsa_slave_phy_connect(slave_dev, p->dp->index);
                if (ret) {
                        netdev_err(slave_dev, "failed to connect to port %d: 
%d\n",
                                   p->dp->index, ret);
                        if (phy_is_fixed)
                                of_phy_deregister_fixed_link(port_dn);
                        return ret;
                }
        }

        return 0;
}