[PATCH] net: dsa: mv88e6xxx: hwtstamp: fix potential negative array index read

[Gustavo A. R. Silva]

_port_ is being used as index to array port_hwtstamp before verifying
it is a non-negative number and a valid index at 209:

if (port < 0 || port >= mv88e6xxx_num_ports(chip))

Fix this by checking _port_ before using it as index to array
port_hwtstamp.

Addresses-Coverity-ID: 1465287 ("Negative array index read")
Fixes: c6fe0ad2c349 ("net: dsa: mv88e6xxx: add rx/tx timestamping support")
Signed-off-by: Gustavo A. R. Silva <garsi...@embeddedor.com>
---
 drivers/net/dsa/mv88e6xxx/hwtstamp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/hwtstamp.c 
b/drivers/net/dsa/mv88e6xxx/hwtstamp.c
index b251d53..761decc 100644
--- a/drivers/net/dsa/mv88e6xxx/hwtstamp.c
+++ b/drivers/net/dsa/mv88e6xxx/hwtstamp.c
@@ -200,8 +200,8 @@ int mv88e6xxx_port_hwtstamp_get(struct dsa_switch *ds, int 
port,
                                struct ifreq *ifr)
 {
        struct mv88e6xxx_chip *chip = ds->priv;
-       struct mv88e6xxx_port_hwtstamp *ps = &chip->port_hwtstamp[port];
-       struct hwtstamp_config *config = &ps->tstamp_config;
+       struct mv88e6xxx_port_hwtstamp *ps;
+       struct hwtstamp_config *config;
 
        if (!chip->info->ptp_support)
                return -EOPNOTSUPP;
@@ -209,6 +209,9 @@ int mv88e6xxx_port_hwtstamp_get(struct dsa_switch *ds, int 
port,
        if (port < 0 || port >= mv88e6xxx_num_ports(chip))
                return -EINVAL;
 
+       ps = &chip->port_hwtstamp[port];
+       config = &ps->tstamp_config;
+
        return copy_to_user(ifr->ifr_data, config, sizeof(*config)) ?
                -EFAULT : 0;
 }
-- 
2.7.4