[PATCH V2 net 12/12] net: ena: ena-com.c: prevent NULL pointer dereference

[<sameehj@amazon.com>]

From: Arthur Kiyanovski <akiyano@amazon.com>

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>
---
 drivers/net/ethernet/amazon/ena/ena_com.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 0f93d1092..1fb58f9ad 100644
--- 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);
-- 
2.24.1.AMZN