[PATCH net-next 1/4] mptcp: options: mpc: avoid printing uninit data

When parsing the MP_CAPABLE suboption, this pr_debug() might read and
print uninitialised values.

That's mostly harmless, but that's also confusing. Fixing that also
avoids some tools to complain about accessing uninit data.

So read these fields only if they have been set.

Note: this was initially reported by Clashiko as an existing issue. The
code has been analysed by a human and confirmed. This is a non-urgent
fix.

Fixes: cc7972ea1932 ("mptcp: parse and emit MP_CAPABLE option according to v1 spec")
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/options.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index c2f4d7bd080c..3b4a22846055 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c

@@ -126,8 +126,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 			ptr += 2;
 		}
 		pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d csum=%u\n",
-			 version, flags, opsize, mp_opt->sndr_key,
-			 mp_opt->rcvr_key, mp_opt->data_len, mp_opt->csum);
+			 version, flags, opsize,
+			 opsize >= TCPOLEN_MPTCP_MPC_SYNACK ? mp_opt->sndr_key : 0,
+			 opsize >= TCPOLEN_MPTCP_MPC_ACK ? mp_opt->rcvr_key : 0,
+			 opsize >= TCPOLEN_MPTCP_MPC_ACK_DATA ? mp_opt->data_len : 0,
+			 opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM ? mp_opt->csum : 0);
 		break;
 
 	case MPTCPOPT_MP_JOIN:

-- 
2.55.0