[PATCH v2] net: alx: fix race condition in alx_remove

[Zekun Shen]

There is a race condition exist during termination. The path is
alx_stop and then alx_remove. An alx_schedule_link_check could be called
before alx_stop by interrupt handler and invoke alx_link_check later.
Alx_stop frees the napis, and alx_remove cancels any pending works.
If any of the work is scheduled before termination and invoked before
alx_remove, a null-ptr-deref occurs because both expect alx->napis[i].

This patch fix the race condition by moving cancel_work_sync functions
before alx_free_napis inside alx_stop. Because interrupt handler can call
alx_schedule_link_check again, alx_free_irq is moved before
cancel_work_sync calls too.

Signed-off-by: Zekun Shen <bruceshe...@gmail.com>
---
Changes in v2:
- move alx_free_irq before cancel_work_sync calls
- prevent another interrupt to cause race condition

 drivers/net/ethernet/atheros/alx/main.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/atheros/alx/main.c 
b/drivers/net/ethernet/atheros/alx/main.c
index b9b4edb91..9b7f1af5f 100644
--- a/drivers/net/ethernet/atheros/alx/main.c
+++ b/drivers/net/ethernet/atheros/alx/main.c
@@ -1249,8 +1249,12 @@ static int __alx_open(struct alx_priv *alx, bool resume)
 
 static void __alx_stop(struct alx_priv *alx)
 {
-       alx_halt(alx);
        alx_free_irq(alx);
+
+       cancel_work_sync(&alx->link_check_wk);
+       cancel_work_sync(&alx->reset_wk);
+
+       alx_halt(alx);
        alx_free_rings(alx);
        alx_free_napis(alx);
 }
@@ -1855,9 +1859,6 @@ static void alx_remove(struct pci_dev *pdev)
        struct alx_priv *alx = pci_get_drvdata(pdev);
        struct alx_hw *hw = &alx->hw;
 
-       cancel_work_sync(&alx->link_check_wk);
-       cancel_work_sync(&alx->reset_wk);
-
        /* restore permanent mac address */
        alx_set_macaddr(hw, hw->perm_addr);
 
-- 
2.17.1