wimax/i2400m: fix bad race condition check in RX path

The i2400m->rx_roq data structure is protected against race conditions
with a reference count (i2400m->rx_roq_refcount); the pointer can be
read-referenced under the i2400m->rx_lock spinlock.

The code in i2400m_rx_edata() wasn't properly following access
protocol, performing an invalid check on i2400m->rx_roq (which is
cleared to NULL when the refcount drops to zero). As such, it was
missing to detect when the data structure is no longer valid and
oopsing with a NULL pointer dereference.

This commit fixes said check by verifying, under the rx_lock spinlock,
that i2400m->rx_roq is non-NULL and then increasing the reference
count before dropping the spinlock.

Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/net/wimax/i2400m/rx.c b/drivers/net/wimax/i2400m/rx.c
index c835ae8b89ce..6cd12d64fc7a 100644
--- a/drivers/net/wimax/i2400m/rx.c
+++ b/drivers/net/wimax/i2400m/rx.c
@@ -1033,12 +1033,12 @@ void i2400m_rx_edata(struct i2400m *i2400m, struct sk_buff *skb_rx,
                 ro_sn = (reorder >> I2400M_RO_SN_SHIFT) & I2400M_RO_SN;
 
                 spin_lock_irqsave(&i2400m->rx_lock, flags);
-                roq = &i2400m->rx_roq[ro_cin];
-                if (roq == NULL) {
+                if (i2400m->rx_roq == NULL) {
                         kfree_skb(skb); /* rx_roq is already destroyed */
                         spin_unlock_irqrestore(&i2400m->rx_lock, flags);
                         goto error;
                 }
+                roq = &i2400m->rx_roq[ro_cin];
                 kref_get(&i2400m->rx_roq_refcount);
                 spin_unlock_irqrestore(&i2400m->rx_lock, flags);