Merge branch 'mptcp-fixes-addressing-syzbot-reports'

Matthieu Baerts says:

====================
mptcp: fixes addressing syzbot reports

Recently, a few issues linked to MPTCP have been reported by syzbot. All
the remaining ones are addressed in this series.

- Patch 1: Address "KMSAN: uninit-value in mptcp_incoming_options (2)".
  A fix for v5.11.

- Patch 2: Address "WARNING in mptcp_pm_nl_set_flags (2)". A fix for
  v5.18.

- Patch 3: Address "WARNING in __mptcp_clean_una (2)". A fix for v6.4,
  backported up to v6.1.
====================

Link: https://patch.msgid.link/20250123-net-mptcp-syzbot-issues-v1-0-af73258a726f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/mptcp/options.c

@@ -108,7 +108,6 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 			mp_opt->suboptions |= OPTION_MPTCP_DSS;
 			mp_opt->use_map = 1;
 			mp_opt->mpc_map = 1;
-			mp_opt->use_ack = 0;
 			mp_opt->data_len = get_unaligned_be16(ptr);
 			ptr += 2;
 		}
@@ -157,11 +156,6 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		pr_debug("DSS\n");
 		ptr++;
 
-		/* we must clear 'mpc_map' be able to detect MP_CAPABLE
-		 * map vs DSS map in mptcp_incoming_options(), and reconstruct
-		 * map info accordingly
-		 */
-		mp_opt->mpc_map = 0;
 		flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
 		mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
 		mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
@@ -369,8 +363,11 @@ void mptcp_get_options(const struct sk_buff *skb,
 	const unsigned char *ptr;
 	int length;
 
-	/* initialize option status */
-	mp_opt->suboptions = 0;
+	/* Ensure that casting the whole status to u32 is efficient and safe */
+	BUILD_BUG_ON(sizeof_field(struct mptcp_options_received, status) != sizeof(u32));
+	BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct mptcp_options_received, status),
+				 sizeof(u32)));
+	*(u32 *)&mp_opt->status = 0;
 
 	length = (th->doff * 4) - sizeof(struct tcphdr);
 	ptr = (const unsigned char *)(th + 1);

net/mptcp/pm_netlink.c

@@ -2020,7 +2020,8 @@ int mptcp_pm_nl_set_flags(struct sk_buff *skb, struct genl_info *info)
 		return -EINVAL;
 	}
 	if ((addr.flags & MPTCP_PM_ADDR_FLAG_FULLMESH) &&
-	    (entry->flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
+	    (entry->flags & (MPTCP_PM_ADDR_FLAG_SIGNAL |
+			     MPTCP_PM_ADDR_FLAG_IMPLICIT))) {
 		spin_unlock_bh(&pernet->lock);
 		GENL_SET_ERR_MSG(info, "invalid addr flags");
 		return -EINVAL;

net/mptcp/protocol.c

@@ -1767,8 +1767,10 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
 		 * see mptcp_disconnect().
 		 * Attempt it again outside the problematic scope.
 		 */
-		if (!mptcp_disconnect(sk, 0))
+		if (!mptcp_disconnect(sk, 0)) {
+			sk->sk_disconnects++;
 			sk->sk_socket->state = SS_UNCONNECTED;
+		}
 	}
 	inet_clear_bit(DEFER_CONNECT, sk);
 

net/mptcp/protocol.h

@@ -149,22 +149,24 @@ struct mptcp_options_received {
 	u32	subflow_seq;
 	u16	data_len;
 	__sum16	csum;
-	u16	suboptions;
+	struct_group(status,
+		u16 suboptions;
+		u16 use_map:1,
+		    dsn64:1,
+		    data_fin:1,
+		    use_ack:1,
+		    ack64:1,
+		    mpc_map:1,
+		    reset_reason:4,
+		    reset_transient:1,
+		    echo:1,
+		    backup:1,
+		    deny_join_id0:1,
+		    __unused:2;
+	);
+	u8	join_id;
 	u32	token;
 	u32	nonce;
-	u16	use_map:1,
-		dsn64:1,
-		data_fin:1,
-		use_ack:1,
-		ack64:1,
-		mpc_map:1,
-		reset_reason:4,
-		reset_transient:1,
-		echo:1,
-		backup:1,
-		deny_join_id0:1,
-		__unused:2;
-	u8	join_id;
 	u64	thmac;
 	u8	hmac[MPTCPOPT_HMAC_LEN];
 	struct mptcp_addr_info addr;