[PATCH 5.4 114/222] bpf: Sockmap/tls, skmsg can have wrapped skmsg that needs extra chaining

[Greg Kroah-Hartman]

From: John Fastabend <john.fastabend@xxxxxxxxx>

commit 9aaaa56845a06aeabdd597cbe19492dc01f281ec upstream.

Its possible through a set of push, pop, apply helper calls to construct
a skmsg, which is just a ring of scatterlist elements, with the start
value larger than the end value. For example,

      end       start
  |_0_|_1_| ... |_n_|_n+1_|

Where end points at 1 and start points and n so that valid elements is
the set {n, n+1, 0, 1}.

Currently, because we don't build the correct chain only {n, n+1} will
be sent. This adds a check and sg_chain call to correctly submit the
above to the crypto and tls send path.

Fixes: d3b18ad31f93d ("tls: add bpf support to sk_msg handling")
Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Jonathan Lemon <jonathan.lemon@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/bpf/20200111061206.8028-8-john.fastabend@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/tls/tls_sw.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -724,6 +724,12 @@ static int tls_push_record(struct sock *
 		sg_mark_end(sk_msg_elem(msg_pl, i));
 	}
 
+	if (msg_pl->sg.end < msg_pl->sg.start) {
+		sg_chain(&msg_pl->sg.data[msg_pl->sg.start],
+			 MAX_SKB_FRAGS - msg_pl->sg.start + 1,
+			 msg_pl->sg.data);
+	}
+
 	i = msg_pl->sg.start;
 	sg_chain(rec->sg_aead_in, 2, &msg_pl->sg.data[i]);