mptcp: mptcp_parse_option() fix for MPTCPOPT_MP_JOIN

mptcp_parse_option() currently sets OPTIONS_MPTCP_MPJ, for the three
possible cases handled for MPTCPOPT_MP_JOIN option.

OPTIONS_MPTCP_MPJ is the combination of three flags:
- OPTION_MPTCP_MPJ_SYN
- OPTION_MPTCP_MPJ_SYNACK
- OPTION_MPTCP_MPJ_ACK

This is a problem, because backup, join_id, token, nonce and/or hmac fields
could be left uninitialized in some cases.

Distinguish the three cases, as following patches will need this step.

Fixes: f296234c ("mptcp: Add handling of incoming MP_JOIN requests")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: Peter Krystad <peter.krystad@linux.intel.com>
Cc: Matthieu Baerts <matttbe@kernel.org>
Cc: Mat Martineau <martineau@kernel.org>
Cc: Geliang Tang <geliang.tang@linux.dev>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240111194917.4044654-2-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/options.c

@@ -123,8 +123,8 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_MP_JOIN:
-		mp_opt->suboptions |= OPTIONS_MPTCP_MPJ;
 		if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_SYN;
 			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
 			mp_opt->join_id = *ptr++;
 			mp_opt->token = get_unaligned_be32(ptr);
@@ -135,6 +135,7 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 				 mp_opt->backup, mp_opt->join_id,
 				 mp_opt->token, mp_opt->nonce);
 		} else if (opsize == TCPOLEN_MPTCP_MPJ_SYNACK) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_SYNACK;
 			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
 			mp_opt->join_id = *ptr++;
 			mp_opt->thmac = get_unaligned_be64(ptr);
@@ -145,11 +146,10 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 				 mp_opt->backup, mp_opt->join_id,
 				 mp_opt->thmac, mp_opt->nonce);
 		} else if (opsize == TCPOLEN_MPTCP_MPJ_ACK) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_ACK;
 			ptr += 2;
 			memcpy(mp_opt->hmac, ptr, MPTCPOPT_HMAC_LEN);
 			pr_debug("MP_JOIN hmac");
-		} else {
-			mp_opt->suboptions &= ~OPTIONS_MPTCP_MPJ;
 		}
 		break;