[net-next PATCH 4/5] udp: Do not copy destructor if one is not present

[Alexander Duyck]

From: Alexander Duyck <alexander.h.du...@intel.com>

This patch makes it so that if a destructor is not present we avoid trying
to update the skb socket or any reference counting that would be associated
with the NULL socket and/or descriptor. By doing this we can support
traffic coming from another namespace without any issues.

Signed-off-by: Alexander Duyck <alexander.h.du...@intel.com>
---
 net/ipv4/udp_offload.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index fd94bbb369b2..52760660d674 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -195,6 +195,7 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
        unsigned int sum_truesize = 0;
        struct udphdr *uh;
        unsigned int mss;
+       bool copy_dtor;
        __sum16 check;
        __be16 newlen;
 
@@ -208,12 +209,14 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
        skb_pull(gso_skb, sizeof(*uh));
 
        /* clear destructor to avoid skb_segment assigning it to tail */
-       WARN_ON_ONCE(gso_skb->destructor != sock_wfree);
+       copy_dtor = gso_skb->destructor == sock_wfree;
+       WARN_ON_ONCE(gso_skb->destructor && !copy_dtor);
        gso_skb->destructor = NULL;
 
        segs = skb_segment(gso_skb, features);
        if (unlikely(IS_ERR_OR_NULL(segs))) {
-               gso_skb->destructor = sock_wfree;
+               if (copy_dtor)
+                       gso_skb->destructor = sock_wfree;
                return segs;
        }
 
@@ -234,9 +237,11 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
                                            (__force u32)newlen));
 
        for (;;) {
-               seg->destructor = sock_wfree;
-               seg->sk = sk;
-               sum_truesize += seg->truesize;
+               if (copy_dtor) {
+                       seg->destructor = sock_wfree;
+                       seg->sk = sk;
+                       sum_truesize += seg->truesize;
+               }
 
                if (!seg->next)
                        break;
@@ -268,7 +273,9 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
                uh->check = gso_make_checksum(seg, ~check);
 
        /* update refcount for the packet */
-       refcount_add(sum_truesize - gso_skb->truesize, &sk->sk_wmem_alloc);
+       if (copy_dtor)
+               refcount_add(sum_truesize - gso_skb->truesize,
+                            &sk->sk_wmem_alloc);
 out:
        return segs;
 }