udp: enable MSG_PEEK at non-zero offset

Enable peeking at UDP datagrams at the offset specified with socket
option SOL_SOCKET/SO_PEEK_OFF. Peek at any datagram in the queue, up
to the end of the given datagram.

Implement the SO_PEEK_OFF semantics introduced in commit ef64a54f6e55
("sock: Introduce the SO_PEEK_OFF sock option"). Increase the offset
on peek, decrease it on regular reads.

When peeking, always checksum the packet immediately, to avoid
recomputation on subsequent peeks and final read.

The socket lock is not held for the duration of udp_recvmsg, so
peek and read operations can run concurrently. Only the last store
to sk_peek_off is preserved.

Signed-off-by: Sam Kumar <samanthakumar@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 15d0df943466..007381270ff8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2949,7 +2949,12 @@ int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 				 struct iov_iter *from, int len);
 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
-void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb);
+void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
+static inline void skb_free_datagram_locked(struct sock *sk,
+					    struct sk_buff *skb)
+{
+	__skb_free_datagram_locked(sk, skb, 0);
+}
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
 int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);