The RFC 8684 mandates that no-data DATA FIN packets should carry
a DSS with 0 sequence number and data len equal to 1. Currently,
on FIN retransmission we re-use the existing mapping; if the previous
fin transmission was part of a partially acked data packet, we could
end-up writing in the egress packet a non-compliant DSS.
The above will be detected by a "Bad mapping" warning on the receiver
side.
This change addresses the issue explicitly checking for 0 len packet
when adding the DATA_FIN option.
Fixes: 6d0060f600ad ("mptcp: Write MPTCP DSS headers to outgoing data packets")
Reported-by: syzbot+42a07faa5923cfaeb...@syzkaller.appspotmail.com
Tested-by: Christoph Paasch <cpaa...@apple.com>
Reviewed-by: Christoph Paasch <cpaa...@apple.com>
Reviewed-by: Mat Martineau <mathew.j.martin...@linux.intel.com>
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
net/mptcp/options.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index df9a51425c6f..8f940be42f98 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -449,9 +449,9 @@ static bool mptcp_established_options_mp(struct sock *sk,
struct sk_buff *skb,
}
static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
- struct mptcp_ext *ext)
+ struct sk_buff *skb, struct mptcp_ext *ext)
{
- if (!ext->use_map) {
+ if (!ext->use_map || !skb->len) {
/* RFC6824 requires a DSS mapping with specific values
* if DATA_FIN is set but no data payload is mapped
*/
@@ -503,7 +503,7 @@ static bool mptcp_established_options_dss(struct sock *sk,
struct sk_buff *skb,
opts->ext_copy = *mpext;
if (skb && tcp_fin && subflow->data_fin_tx_enable)
- mptcp_write_data_fin(subflow, &opts->ext_copy);
+ mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
ret = true;
}
--
2.26.2
