[patch net-next 3/3] fix skb_morph to preserve skb->sk and skb->destructor pointers

[Jiri Pirko <jiri@xxxxxxxxxxx>]

Currently __skb_clone sets skb->sk and skb->destructor to NULL. This is
not right for skb_morph use case because skb->sk may be previously
set (e. g. by xt_TPROXY).

Also, during skb_morph the destructor should not be called. It might be
previously set, e. g. by xt_TPROXY to sock_edemux, and that would cause
put sk while skb is still in flight.

This patch fixes these.

Signed-off-by: Jiri Pirko <jiri@xxxxxxxxxxx>
---
 net/core/skbuff.c | 44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3735fad..21b320e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -515,7 +515,7 @@ static void skb_free_head(struct sk_buff *skb)
 		kfree(skb->head);
 }
 
-static void skb_release_data(struct sk_buff *skb)
+static void __skb_release_data(struct sk_buff *skb)
 {
 	if (!skb->cloned ||
 	    !atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
@@ -579,16 +579,12 @@ static void kfree_skbmem(struct sk_buff *skb)
 	}
 }
 
-static void skb_release_head_state(struct sk_buff *skb)
+static void __skb_release_head_state(struct sk_buff *skb)
 {
 	skb_dst_drop(skb);
 #ifdef CONFIG_XFRM
 	secpath_put(skb->sp);
 #endif
-	if (skb->destructor) {
-		WARN_ON(in_irq());
-		skb->destructor(skb);
-	}
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 	nf_conntrack_put(skb->nfct);
 #endif
@@ -607,12 +603,19 @@ static void skb_release_head_state(struct sk_buff *skb)
 #endif
 }
 
-/* Free everything but the sk_buff shell. */
-static void skb_release_all(struct sk_buff *skb)
+static void skb_release_head_state(struct sk_buff *skb)
+{
+	if (skb->destructor) {
+		WARN_ON(in_irq());
+		skb->destructor(skb);
+	}
+	__skb_release_head_state(skb);
+}
+
+static void skb_release_data(struct sk_buff *skb)
 {
-	skb_release_head_state(skb);
 	if (likely(skb->head))
-		skb_release_data(skb);
+		__skb_release_data(skb);
 }
 
 /**
@@ -626,7 +629,8 @@ static void skb_release_all(struct sk_buff *skb)
 
 void __kfree_skb(struct sk_buff *skb)
 {
-	skb_release_all(skb);
+	skb_release_head_state(skb);
+	skb_release_data(skb);
 	kfree_skbmem(skb);
 }
 EXPORT_SYMBOL(__kfree_skb);
@@ -761,12 +765,11 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
  * You should not add any new code to this function.  Add it to
  * __copy_skb_header above instead.
  */
-static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
+static struct sk_buff *___skb_clone(struct sk_buff *n, struct sk_buff *skb)
 {
 #define C(x) n->x = skb->x
 
 	n->next = n->prev = NULL;
-	n->sk = NULL;
 	__copy_skb_header(n, skb);
 
 	C(len);
@@ -775,7 +778,6 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 	n->hdr_len = skb->nohdr ? skb_headroom(skb) : skb->hdr_len;
 	n->cloned = 1;
 	n->nohdr = 0;
-	n->destructor = NULL;
 	C(tail);
 	C(end);
 	C(head);
@@ -791,6 +793,13 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 #undef C
 }
 
+static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
+{
+	n->sk = NULL;
+	n->destructor = NULL;
+	return ___skb_clone(n, skb);
+}
+
 /**
  *	skb_morph	-	morph one skb into another
  *	@dst: the skb to receive the contents
@@ -803,8 +812,9 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
  */
 struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
 {
-	skb_release_all(dst);
-	return __skb_clone(dst, src);
+	__skb_release_head_state(dst);
+	skb_release_data(dst);
+	return ___skb_clone(dst, src);
 }
 EXPORT_SYMBOL_GPL(skb_morph);
 
@@ -1107,7 +1117,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		if (skb_has_frag_list(skb))
 			skb_clone_fraglist(skb);
 
-		skb_release_data(skb);
+		__skb_release_data(skb);
 	} else {
 		skb_free_head(skb);
 	}
-- 
1.8.3.1

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