diff mbox

Double free of dst_entry in ipv4_dst_destroy()

Message ID 1449453515.25029.54.camel@edumazet-glaptop2.roam.corp.google.com
State RFC, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Dec. 7, 2015, 1:58 a.m. UTC 
On Sun, 2015-12-06 at 13:03 -0800, Eric Dumazet wrote:

> But then when later we promote a skb->dst to a refctounted one
> (skb_dst_force(), we might make sure we abort the operation if __refcnt
> == 0 ( and DST_NOCACHE is in dst->flags)
> 

Minimum patch would be :



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diff mbox

Patch

diff --git a/include/net/dst.h b/include/net/dst.h
index 1279f9b09791..b9a3239f4296 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -322,6 +322,24 @@  static inline void skb_dst_force(struct sk_buff *skb)
 	}
 }
 
+/**
+ * skb_dst_force_safe - makes sure skb dst is refcounted
+ * @skb: buffer
+ *
+ * If dst is not yet refcounted and not destroyed, grab a ref on it.
+ */
+static inline void skb_dst_force_safe(struct sk_buff *skb)
+{
+	if (skb_dst_is_noref(skb)) {
+		struct dst_entry *dst = skb_dst(skb);
+
+		if (!atomic_inc_not_zero(&dst->__refcnt))
+			dst = NULL;
+
+		skb->_skb_refdst = (unsigned long)dst;
+	}
+}
+
 
 /**
  *	__skb_tunnel_rx - prepare skb for rx reinsert
diff --git a/include/net/sock.h b/include/net/sock.h
index b1d475b5db68..6367d1112c3d 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -816,7 +816,7 @@  void sk_stream_write_space(struct sock *sk);
 static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
 {
 	/* dont let skb dst not refcounted, we are going to leave rcu lock */
-	skb_dst_force(skb);
+	skb_dst_force_safe(skb);
 
 	if (!sk->sk_backlog.tail)
 		sk->sk_backlog.head = skb;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index db003438aaf5..a72688a288f5 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1493,7 +1493,7 @@  bool tcp_prequeue(struct sock *sk, struct sk_buff *skb)
 	if (likely(sk->sk_rx_dst))
 		skb_dst_drop(skb);
 	else
-		skb_dst_force(skb);
+		skb_dst_force_safe(skb);
 
 	__skb_queue_tail(&tp->ucopy.prequeue, skb);
 	tp->ucopy.memory += skb->truesize;