rxrpc: Fix potential data race in rxrpc_wait_to_be_connected()

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix potential data race in rxrpc_wait_to_be_connected()

Inside the loop in rxrpc_wait_to_be_connected() it checks call->error to

see if it should exit the loop without first checking the call state. This

is probably safe as if call->error is set, the call is dead anyway, but we

should probably wait for the call state to have been set to completion

first, lest it cause surprise on the way out.

Fix this by only accessing call->error if the call is complete. We don't

actually need to access the error inside the loop as we'll do that after.

This caused the following report:

BUG: KCSAN: data-race in rxrpc_send_data / rxrpc_set_call_completion

write to 0xffff888159cf3c50 of 4 bytes by task 25673 on cpu 1:

rxrpc_set_call_completion+0x71/0x1c0 net/rxrpc/call_state.c:22

rxrpc_send_data_packet+0xba9/0x1650 net/rxrpc/output.c:479

rxrpc_transmit_one+0x1e/0x130 net/rxrpc/output.c:714

rxrpc_decant_prepared_tx net/rxrpc/call_event.c:326 [inline]

rxrpc_transmit_some_data+0x496/0x600 net/rxrpc/call_event.c:350

rxrpc_input_call_event+0x564/0x1220 net/rxrpc/call_event.c:464

rxrpc_io_thread+0x307/0x1d80 net/rxrpc/io_thread.c:461

kthread+0x1ac/0x1e0 kernel/kthread.c:376

ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

read to 0xffff888159cf3c50 of 4 bytes by task 25672 on cpu 0:

rxrpc_send_data+0x29e/0x1950 net/rxrpc/sendmsg.c:296

rxrpc_do_sendmsg+0xb7a/0xc20 net/rxrpc/sendmsg.c:726

rxrpc_sendmsg+0x413/0x520 net/rxrpc/af_rxrpc.c:565

sock_sendmsg_nosec net/socket.c:724 [inline]

sock_sendmsg net/socket.c:747 [inline]

____sys_sendmsg+0x375/0x4c0 net/socket.c:2501

___sys_sendmsg net/socket.c:2555 [inline]

__sys_sendmmsg+0x263/0x500 net/socket.c:2641

__do_sys_sendmmsg net/socket.c:2670 [inline]

__se_sys_sendmmsg net/socket.c:2667 [inline]

__x64_sys_sendmmsg+0x57/0x60 net/socket.c:2667

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000000 -> 0xffffffea