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Date:   Thu, 15 Feb 2018 12:10:05 -0600
From:   "Gustavo A. R. Silva" <garsilva@embeddedor.com>
To:     Brandon Streiff <brandon.streiff@ni.com>,
        Andrew Lunn <andrew@lunn.ch>,
        Vivien Didelot <vivien.didelot@savoirfairelinux.com>,
        Florian Fainelli <f.fainelli@gmail.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <garsilva@embeddedor.com>
Subject: [PATCH] net: dsa: mv88e6xxx: hwtstamp: fix potential negative array
 index read
Message-ID: <20180215181005.GA21263@embeddedor.com>
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_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 <garsilva@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