net/tls: fully initialize the msg wrapper skb

If strparser gets cornered into starting a new message from
an sk_buff which already has frags, it will allocate a new
skb to become the "wrapper" around the fragments of the
message.

This new skb does not inherit any metadata fields.  In case
of TLS offload this may lead to unnecessarily re-encrypting
the message, as skb->decrypted is not set for the wrapper skb.

Try to be conservative and copy all fields of old skb
strparser's user may reasonably need.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1063,6 +1063,7 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
 				     int max_page_order,
 				     int *errcode,
 				     gfp_t gfp_mask);
+struct sk_buff *alloc_skb_for_msg(struct sk_buff *first);
 
 /* Layout of fast clones : [skb1][skb2][fclone_ref] */
 struct sk_buff_fclones {

net/core/skbuff.c

@@ -913,6 +913,31 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 #undef C
 }
 
+/**
+ * alloc_skb_for_msg() - allocate sk_buff to wrap frag list forming a msg
+ * @first: first sk_buff of the msg
+ */
+struct sk_buff *alloc_skb_for_msg(struct sk_buff *first)
+{
+	struct sk_buff *n;
+
+	n = alloc_skb(0, GFP_ATOMIC);
+	if (!n)
+		return NULL;
+
+	n->len = first->len;
+	n->data_len = first->len;
+	n->truesize = first->truesize;
+
+	skb_shinfo(n)->frag_list = first;
+
+	__copy_skb_header(n, first);
+	n->destructor = NULL;
+
+	return n;
+}
+EXPORT_SYMBOL_GPL(alloc_skb_for_msg);
+
 /**
  *	skb_morph	-	morph one skb into another
  *	@dst: the skb to receive the contents

net/strparser/strparser.c

@@ -160,18 +160,14 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
 					return 0;
 				}
 
-				skb = alloc_skb(0, GFP_ATOMIC);
+				skb = alloc_skb_for_msg(head);
 				if (!skb) {
 					STRP_STATS_INCR(strp->stats.mem_fail);
 					desc->error = -ENOMEM;
 					return 0;
 				}
-				skb->len = head->len;
-				skb->data_len = head->len;
-				skb->truesize = head->truesize;
-				*_strp_msg(skb) = *_strp_msg(head);
+
 				strp->skb_nextp = &head->next;
-				skb_shinfo(skb)->frag_list = head;
 				strp->skb_head = skb;
 				head = skb;
 			} else {