Re: [PATCH NET-NEXT] ipv6: skb_expand_head() adjust skb->truesize incorrectly

Christoph Paasch reports [1] about incorrect skb->truesize
after skb_expand_head() call in ip6_xmit.
This happen because skb_set_owner_w() for newly clone skb is called
too early, before pskb_expand_head() where truesize is adjusted for
(!skb-sk) case.

[1] https://lkml.org/lkml/2021/8/20/1082

Reported-by: Christoph Paasch <redacted>
Signed-off-by: Vasily Averin <redacted>
---
 net/core/skbuff.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f931176..508d5c4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -1803,6 +1803,8 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)

 struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
 {
+       struct sk_buff *oskb = skb;
+       struct sk_buff *nskb = NULL;
        int delta = headroom - skb_headroom(skb);

        if (WARN_ONCE(delta <= 0,

@@ -1811,21 +1813,21 @@ struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)

        /* pskb_expand_head() might crash, if skb is shared */
        if (skb_shared(skb)) {
-               struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
-
-               if (likely(nskb)) {
-                       if (skb->sk)
-                               skb_set_owner_w(nskb, skb->sk);
-                       consume_skb(skb);
-               } else {
-                       kfree_skb(skb);
-               }
+               nskb = skb_clone(skb, GFP_ATOMIC);
                skb = nskb;
        }
        if (skb &&
-           pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
-               kfree_skb(skb);
+           pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC))
                skb = NULL;
+
+       if (!skb) {
+               kfree_skb(oskb);
+               if (nskb)
+                       kfree_skb(nskb);
+       } else if (nskb) {
+               if (oskb->sk)
+                       skb_set_owner_w(nskb, oskb->sk);
+               consume_skb(oskb);