[PATCH 1/2] net: Stop decapitating clones that have a head_frag

Alexander Duyck
2012-05-03T03:38:42Z

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>
---

net/core/skbuff.c | 2 +-
net/ipv4/tcp_input.c | 9 ++-------
2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 52ba2b5..8703754 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1699,7 +1699,7 @@ 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_linear = !skb->head_frag || skb_cloned(skb);

/* map the linear part :
* If skb->head_frag is set, this 'linear' part is backed
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2f696ef..c6f78e2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4589,7 +4589,7 @@ copyfrags:
to->data_len += len;
goto merge;
}
- if (from->head_frag) {
+ if (from->head_frag && !skb_cloned(from)) {
struct page *page;
unsigned int offset;

@@ -4599,12 +4599,7 @@ copyfrags:
offset = from->data - (unsigned char *)page_address(page);
skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
page, offset, skb_headlen(from));
-
- if (skb_cloned(from))
- get_page(page);
- else
- *fragstolen = true;
-
+ *fragstolen = true;
delta = len; /* we dont know real truesize... */
goto copyfrags;
}