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

From: Joe Perches
Date: Sat Sep 23 2017 - 13:13:16 EST


On Sat, 2017-09-23 at 17:57 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> 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.king@xxxxxxxxxxxxx>
> ---
> 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;
}