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From:   Zekun Shen <bruceshenzk@gmail.com>
Cc:     Zekun Shen <bruceshenzk@gmail.com>,
        Jay Cliburn <jcliburn@gmail.com>,
        Chris Snook <chris.snook@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] net: alx: fix race condition in alx_remove
Date:   Sun, 14 Jun 2020 12:59:12 -0400
Message-Id: <20200614165912.25622-1-bruceshenzk@gmail.com>
To:     unlisted-recipients:; (no To-header on input)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 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.

Signed-off-by: Zekun Shen <bruceshenzk@gmail.com>
---
 drivers/net/ethernet/atheros/alx/main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/atheros/alx/main.c b/drivers/net/ethernet/atheros/alx/main.c
index b9b4edb91..1487d6765 100644
--- a/drivers/net/ethernet/atheros/alx/main.c
+++ b/drivers/net/ethernet/atheros/alx/main.c
@@ -1249,6 +1249,9 @@ static int __alx_open(struct alx_priv *alx, bool resume)
 
 static void __alx_stop(struct alx_priv *alx)
 {
+	cancel_work_sync(&alx->link_check_wk);
+	cancel_work_sync(&alx->reset_wk);
+
 	alx_halt(alx);
 	alx_free_irq(alx);
 	alx_free_rings(alx);
@@ -1855,9 +1858,6 @@ 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