netdev - [PATCH net] sfc: fix null pointer dereference in efx_hard_start

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Date:   Wed, 14 Sep 2022 13:11:35 +0200
From:   Íñigo Huguet <ihuguet@...hat.com>
To:     ecree.xilinx@...il.com, habetsm.xilinx@...il.com
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        Íñigo Huguet <ihuguet@...hat.com>,
        Tianhao Zhao <tizhao@...hat.com>
Subject: [PATCH net] sfc: fix null pointer dereference in efx_hard_start_xmit

Trying to get the channel from the tx_queue variable here is wrong
because we can only be here if tx_queue is NULL, so we shouldn't
dereference it. As the above comment in the code says, this is very
unlikely to happen, but it's wrong anyway so let's fix it.

I hit this issue because of a different bug that caused tx_queue to be
NULL. If that happens, this is the error message that we get here:
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
  [...]
  RIP: 0010:efx_hard_start_xmit+0x153/0x170 [sfc]

Fixes: 12804793b17c ("sfc: decouple TXQ type from label")
Reported-by: Tianhao Zhao <tizhao@...hat.com>
Signed-off-by: Íñigo Huguet <ihuguet@...hat.com>
---
 drivers/net/ethernet/sfc/tx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index d12474042c84..c5f88f7a7a04 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -549,7 +549,7 @@ netdev_tx_t efx_hard_start_xmit(struct sk_buff *skb,
 		 * previous packets out.
 		 */
 		if (!netdev_xmit_more())
-			efx_tx_send_pending(tx_queue->channel);
+			efx_tx_send_pending(efx_get_tx_channel(efx, index));
 		return NETDEV_TX_OK;
 	}

-- 
2.34.1