__netif_receive_skb_core: pass skb by reference

__netif_receive_skb_core may change the skb pointer passed into it (e.g.
in rx_handler). The original skb may be freed as a result of this
operation.

The callers of __netif_receive_skb_core may further process original skb
by using pt_prev pointer returned by __netif_receive_skb_core thus
leading to unpleasant effects.

The solution is to pass skb by reference into __netif_receive_skb_core.

v2: Added Fixes tag and comment regarding ppt_prev and skb invariant.

Fixes: 88eb1944e18c ("net: core: propagate SKB lists through packet_type lookup")
Signed-off-by: Boris Sukholitko <boris.sukholitko@broadcom.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 6d327b7..2d8acee 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4988,11 +4988,12 @@ static inline int nf_ingress(struct sk_buff *skb, struct packet_type **pt_prev,
        return 0;
 }
 
-static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc,
+static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
                                    struct packet_type **ppt_prev)
 {
        struct packet_type *ptype, *pt_prev;
        rx_handler_func_t *rx_handler;
+       struct sk_buff *skb = *pskb;
        struct net_device *orig_dev;
        bool deliver_exact = false;
        int ret = NET_RX_DROP;
@@ -5023,8 +5024,10 @@ another_round:
                ret2 = do_xdp_generic(rcu_dereference(skb->dev->xdp_prog), skb);
                preempt_enable();
 
-               if (ret2 != XDP_PASS)
-                       return NET_RX_DROP;
+               if (ret2 != XDP_PASS) {
+                       ret = NET_RX_DROP;
+                       goto out;
+               }
                skb_reset_mac_len(skb);
        }
 
@@ -5174,6 +5177,13 @@ drop:
        }
 
 out:
+       /* The invariant here is that if *ppt_prev is not NULL
+        * then skb should also be non-NULL.
+        *
+        * Apparently *ppt_prev assignment above holds this invariant due to
+        * skb dereferencing near it.
+        */
+       *pskb = skb;
        return ret;
 }
 
@@ -5183,7 +5193,7 @@ static int __netif_receive_skb_one_core(struct sk_buff *skb, bool pfmemalloc)
        struct packet_type *pt_prev = NULL;
        int ret;
 
-       ret = __netif_receive_skb_core(skb, pfmemalloc, &pt_prev);
+       ret = __netif_receive_skb_core(&skb, pfmemalloc, &pt_prev);
        if (pt_prev)
                ret = INDIRECT_CALL_INET(pt_prev->func, ipv6_rcv, ip_rcv, skb,
                                         skb->dev, pt_prev, orig_dev);
@@ -5261,7 +5271,7 @@ static void __netif_receive_skb_list_core(struct list_head *head, bool pfmemallo
                struct packet_type *pt_prev = NULL;
 
                skb_list_del_init(skb);
-               __netif_receive_skb_core(skb, pfmemalloc, &pt_prev);
+               __netif_receive_skb_core(&skb, pfmemalloc, &pt_prev);
                if (!pt_prev)
                        continue;
                if (pt_curr != pt_prev || od_curr != orig_dev) {