netdev - [PATCH] xfrm : lock input tasklet skb queue

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Date:   Sun, 20 Oct 2019 08:46:10 -0700
From:   Tom Rix <trix@...hat.com>
To:     steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] xfrm : lock input tasklet skb queue

On PREEMPT_RT_FULL while running netperf, a corruption
of the skb queue causes an oops.

This appears to be caused by a race condition here
        __skb_queue_tail(&trans->queue, skb);
        tasklet_schedule(&trans->tasklet);
Where the queue is changed before the tasklet is locked by
tasklet_schedule.

The fix is to use the skb queue lock.

Signed-off-by: Tom Rix <trix@...hat.com>
---
 net/xfrm/xfrm_input.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 9b599ed66d97..226dead86828 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -758,12 +758,16 @@ static void xfrm_trans_reinject(unsigned long data)
     struct xfrm_trans_tasklet *trans = (void *)data;
     struct sk_buff_head queue;
     struct sk_buff *skb;
+    unsigned long flags;

     __skb_queue_head_init(&queue);
+    spin_lock_irqsave(&trans->queue.lock, flags);
     skb_queue_splice_init(&trans->queue, &queue);

     while ((skb = __skb_dequeue(&queue)))
         XFRM_TRANS_SKB_CB(skb)->finish(dev_net(skb->dev), NULL, skb);
+
+    spin_unlock_irqrestore(&trans->queue.lock, flags);
 }

 int xfrm_trans_queue(struct sk_buff *skb,
@@ -771,15 +775,20 @@ int xfrm_trans_queue(struct sk_buff *skb,
                    struct sk_buff *))
 {
     struct xfrm_trans_tasklet *trans;
+    unsigned long flags;

     trans = this_cpu_ptr(&xfrm_trans_tasklet);
+    spin_lock_irqsave(&trans->queue.lock, flags);

-    if (skb_queue_len(&trans->queue) >= netdev_max_backlog)
+    if (skb_queue_len(&trans->queue) >= netdev_max_backlog) {
+        spin_unlock_irqrestore(&trans->queue.lock, flags);
         return -ENOBUFS;
+    }

     XFRM_TRANS_SKB_CB(skb)->finish = finish;
     __skb_queue_tail(&trans->queue, skb);
     tasklet_schedule(&trans->tasklet);
+    spin_unlock_irqrestore(&trans->queue.lock, flags);
     return 0;
 }
 EXPORT_SYMBOL(xfrm_trans_queue);
-- 
2.23.0