net: ena: ena-com.c: prevent NULL pointer dereference

comp_ctx can be NULL in a very rare case when an admin command is executed
during the execution of ena_remove().

The bug scenario is as follows:

* ena_destroy_device() sets the comp_ctx to be NULL
* An admin command is executed before executing unregister_netdev(),
  this can still happen because our device can still receive callbacks
  from the netdev infrastructure such as ethtool commands.
* When attempting to access the comp_ctx, the bug occurs since it's set
  to NULL

Fix:
Added a check that comp_ctx is not NULL

Fixes: 1738cd3ed342 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 0f93d1092435d6a3111a08d6e4d7991d68a4f408..1fb58f9ad80b83243455e5a8d80501a692c80ff6 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -200,6 +200,11 @@ static void comp_ctxt_release(struct ena_com_admin_queue *queue,
 static struct ena_comp_ctx *get_comp_ctxt(struct ena_com_admin_queue *queue,
                                          u16 command_id, bool capture)
 {
+       if (unlikely(!queue->comp_ctx)) {
+               pr_err("Completion context is NULL\n");
+               return NULL;
+       }
+
        if (unlikely(command_id >= queue->q_depth)) {
                pr_err("command id is larger than the queue size. cmd_id: %u queue size %d\n",
                       command_id, queue->q_depth);