[PPPOL2TP]: Fix SMP issues in skb reorder queue handling

When walking a session's packet reorder queue, use
skb_queue_walk_safe() since the list could be modified inside the
loop.

Rearrange the unlinking skbs from the reorder queue such that it is
done while the queue lock is held in pppol2tp_recv_dequeue() when
walking the skb list.

A version of this patch was suggested by Jarek Poplawski.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/net/pppol2tp.c b/drivers/net/pppol2tp.c
index 9a90cede0ecc..3d10ca050b79 100644
--- a/drivers/net/pppol2tp.c
+++ b/drivers/net/pppol2tp.c
@@ -342,10 +342,11 @@ static struct pppol2tp_tunnel *pppol2tp_tunnel_find(u16 tunnel_id)
 static void pppol2tp_recv_queue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
 {
         struct sk_buff *skbp;
+        struct sk_buff *tmp;
         u16 ns = PPPOL2TP_SKB_CB(skb)->ns;
 
         spin_lock_bh(&session->reorder_q.lock);
-        skb_queue_walk(&session->reorder_q, skbp) {
+        skb_queue_walk_safe(&session->reorder_q, skbp, tmp) {
                 if (PPPOL2TP_SKB_CB(skbp)->ns > ns) {
                         __skb_insert(skb, skbp->prev, skbp, &session->reorder_q);
                         PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
@@ -371,10 +372,9 @@ static void pppol2tp_recv_dequeue_skb(struct pppol2tp_session *session, struct s
         int length = PPPOL2TP_SKB_CB(skb)->length;
         struct sock *session_sock = NULL;
 
-        /* We're about to requeue the skb, so unlink it and return resources
+        /* We're about to requeue the skb, so return resources
          * to its current owner (a socket receive buffer).
          */
-        skb_unlink(skb, &session->reorder_q);
         skb_orphan(skb);
 
         tunnel->stats.rx_packets++;
@@ -470,6 +470,11 @@ static void pppol2tp_recv_dequeue(struct pppol2tp_session *session)
                                 goto out;
                         }
                 }
+                __skb_unlink(skb, &session->reorder_q);
+
+                /* Process the skb. We release the queue lock while we
+                 * do so to let other contexts process the queue.
+                 */
                 spin_unlock_bh(&session->reorder_q.lock);
                 pppol2tp_recv_dequeue_skb(session, skb);
                 spin_lock_bh(&session->reorder_q.lock);