[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>

diff --git a/drivers/net/pppol2tp.c b/drivers/net/pppol2tp.c
index 9a90cede0ecc3d73e31373609fb9dcef64a319ad..3d10ca050b7991b9f53cf4a6cc3d5adb873137aa 100644 (file)
--- 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);