In the Linux kernel, the following vulnerability has been resolved:
mptcp: remove tcp ulp setsockopt support
TCP_ULP setsockopt cannot be used for mptcp because its already used internally to plumb subflow (tcp) sockets to the mptcp layer.
syzbot managed to trigger a crash for mptcp connections that are in fallback mode:
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] CPU: 1 PID: 1083 Comm: syz-executor.3 Not tainted 5.16.0-rc2-syzkaller #0 RIP: 0010:tlsbuildproto net/tls/tlsmain.c:776 [inline] [..] _tcpsetulp net/ipv4/tcpulp.c:139 [inline] tcpsetulp+0x428/0x4c0 net/ipv4/tcpulp.c:160 dotcpsetsockopt+0x455/0x37c0 net/ipv4/tcp.c:3391 mptcp_setsockopt+0x1b47/0x2400 net/mptcp/sockopt.c:638
Remove support for TCP_ULP setsockopt.