mqprio: fix potential null pointer dereference on opt

The pointer opt has a null check however before for this check opt is
dereferenced when len is initialized, hence we potentially have a null
pointer deference on opt.  Avoid this by checking for a null opt before
dereferencing it.

Detected by CoverityScan, CID#1458234 ("Dereference before null check")

Fixes: 4e8b86c06269 ("mqprio: Introduce new hardware offload mode and shaper in mqprio")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index cae91b4b08a6..51c2b289c69b 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -142,7 +142,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt)
         struct nlattr *tb[TCA_MQPRIO_MAX + 1];
         struct nlattr *attr;
         int rem;
-        int len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
+        int len;
 
         BUILD_BUG_ON(TC_MAX_QUEUE != TC_QOPT_MAX_QUEUE);
         BUILD_BUG_ON(TC_BITMASK != TC_QOPT_BITMASK);
@@ -164,6 +164,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt)
         if (mqprio_parse_opt(dev, qopt))
                 return -EINVAL;
 
+        len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
         if (len > 0) {
                 err = parse_attr(tb, TCA_MQPRIO_MAX, opt, mqprio_policy,
                                  sizeof(*qopt));