mptcp: prevent BPF accessing lowat from a subflow socket.

Alexei reported the following splat:

 WARNING: CPU: 32 PID: 3276 at net/mptcp/subflow.c:1430 subflow_data_ready+0x147/0x1c0
 Modules linked in: dummy bpf_testmod(O) [last unloaded: bpf_test_no_cfi(O)]
 CPU: 32 PID: 3276 Comm: test_progs Tainted: GO       6.8.0-12873-g2c43c33bfd23
 Call Trace:
  <TASK>
  mptcp_set_rcvlowat+0x79/0x1d0
  sk_setsockopt+0x6c0/0x1540
  __bpf_setsockopt+0x6f/0x90
  bpf_sock_ops_setsockopt+0x3c/0x90
  bpf_prog_509ce5db2c7f9981_bpf_test_sockopt_int+0xb4/0x11b
  bpf_prog_dce07e362d941d2b_bpf_test_socket_sockopt+0x12b/0x132
  bpf_prog_348c9b5faaf10092_skops_sockopt+0x954/0xe86
  __cgroup_bpf_run_filter_sock_ops+0xbc/0x250
  tcp_connect+0x879/0x1160
  tcp_v6_connect+0x50c/0x870
  mptcp_connect+0x129/0x280
  __inet_stream_connect+0xce/0x370
  inet_stream_connect+0x36/0x50
  bpf_trampoline_6442491565+0x49/0xef
  inet_stream_connect+0x5/0x50
  __sys_connect+0x63/0x90
  __x64_sys_connect+0x14/0x20

The root cause of the issue is that bpf allows accessing mptcp-level
proto_ops from a tcp subflow scope.

Fix the issue detecting the problematic call and preventing any action.

Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/482
Fixes: 5684ab1a0eff ("mptcp: give rcvlowat some love")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/d8cb7d8476d66cb0812a6e29cd1e626869d9d53e.1711738080.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index dcd1c76d2a3ba1ccc31a3e9279f725cd6d433782..73fdf423de44eef5d2c3085515ad475bf63fb718 100644 (file)
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1493,6 +1493,10 @@ int mptcp_set_rcvlowat(struct sock *sk, int val)
        struct mptcp_subflow_context *subflow;
        int space, cap;
 
+       /* bpf can land here with a wrong sk type */
+       if (sk->sk_protocol == IPPROTO_TCP)
+               return -EINVAL;
+
        if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
                cap = sk->sk_rcvbuf >> 1;
        else