rust_binder: reject context manager self-transaction

rust_binder: reject context manager self-transaction

Rust binder resolved handle 0 to the context manager node, but it does not
reject the case where the caller owns the same node.

The C binder driver rejects transactions from the context-manager process
to handle 0 after resolving the target node. Match that behavior in Rust
Binder by rejecting handle 0 transactions when the resolved context-manager
node is owned by the calling process.

This applies to both synchronous and oneway transactions because both paths
resolve the target through Process::get_transaction_node().

Cc: stable <stable@kernel.org>
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
Signed-off-by: Keshav Verma <iganschel@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260625103957.730-1-iganschel@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>