[PATCH net v3] net: ngbe: fix NULL pointer dereference in non-MSI-X interrupt enabling

In non-MSI-X mode (such as legacy INTx or single MSI), wx->msix_entry is
not allocated or initialized. Calling NGBE_INTR_MISC(wx) dereferences
wx->msix_entry->entry, leading to a NULL pointer dereference crash.

This issue was introduced by fixing the IRQ vector when the number of
VFs is 7. Fix the issue by explicitly checking `pdev->msix_enabled` to
determine the correct vector index.

Additionally, as a side fix, set the interrupt mask to BIT(0) for the
non-MSI-X fallback. In MSI/INTx mode, the MISC and queue interrupts
share vector 0, and the WX_PX_MISC_IVAR register is only valid in the
MSI-X case. Thus, BIT(0) is the correct mask for the miscellaneous cause
when MSI-X is disabled.

Fixes: 4174c0c331a2 ("net: ngbe: specify IRQ vector when the number of VFs is 7")
Signed-off-by: Jiawen Wu <[email protected]>
Reviewed-by: Breno Leitao <[email protected]>
---
v2 -> v3: Detail the commit log.
v1 -> v2: Use pdev->msix_enabled and reserve NGBE_INTR_MISC.
---
 drivers/net/ethernet/wangxun/ngbe/ngbe_main.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/wangxun/ngbe/ngbe_main.c b/drivers/net/ethernet/wangxun/ngbe/ngbe_main.c
index a16221995909..cb653861aad8 100644
--- a/drivers/net/ethernet/wangxun/ngbe/ngbe_main.c
+++ b/drivers/net/ethernet/wangxun/ngbe/ngbe_main.c
@@ -180,8 +180,10 @@ static void ngbe_irq_enable(struct wx *wx, bool queues)
 	/* mask interrupt */
 	if (queues)
 		wx_intr_enable(wx, NGBE_INTR_ALL);
-	else
+	else if (wx->pdev->msix_enabled)
 		wx_intr_enable(wx, NGBE_INTR_MISC(wx));
+	else
+		wx_intr_enable(wx, BIT(0));
 }
 
 /**
-- 
2.51.0