net: Stop decapitating clones that have a head_frag

This change is meant ot prevent stealing the skb->head to use as a page in
the event that the skb->head was cloned.  This allows the other clones to
track each other via shinfo->dataref.

Without this we break down to two methods for tracking the reference count,
one being dataref, the other being the page count.  As a result it becomes
difficult to track how many references there are to skb->head.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 52ba2b5e803d..9e8caa0c4f72 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1699,17 +1699,18 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
                               struct splice_pipe_desc *spd, struct sock *sk)
 {
         int seg;
-        bool head_is_linear = !skb->head_frag;
+        bool head_is_locked = !skb->head_frag || skb_cloned(skb);
 
         /* map the linear part :
-         * If skb->head_frag is set, this 'linear' part is backed
-         * by a fragment, and we can avoid a copy.
+         * If skb->head_frag is set, this 'linear' part is backed by a
+         * fragment, and if the head is not shared with any clones then
+         * we can avoid a copy since we own the head portion of this page.
          */
         if (__splice_segment(virt_to_page(skb->data),
                              (unsigned long) skb->data & (PAGE_SIZE - 1),
                              skb_headlen(skb),
                              offset, len, skb, spd,
-                             head_is_linear,
+                             head_is_locked,
                              sk, pipe))
                 return true;