mptcp: pm: avoid possible UaF when selecting endp

commit 48e50dcbcbaaf713d82bf2da5c16aeced94ad07d upstream.

select_local_address() and select_signal_address() both select an
endpoint entry from the list inside an RCU protected section, but return
a reference to it, to be read later on. If the entry is dereferenced
after the RCU unlock, reading info could cause a Use-after-Free.

A simple solution is to copy the required info while inside the RCU
protected section to avoid any risk of UaF later. The address ID might
need to be modified later to handle the ID0 case later, so a copy seems
OK to deal with.

Reported-by: Paolo Abeni <pabeni@redhat.com>
Closes: https://lore.kernel.org/45cd30d3-7710-491c-ae4d-a1368c00beb1@redhat.com
Fixes: 01cacb00

 ("mptcp: add netlink-based PM")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-14-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in pm_netlink.c, because the context has been modified in
  commit b9d69db8

 ("mptcp: let the in-kernel PM use mixed IPv4 and
  IPv6 addresses"), which is not a candidate for the backports. The same
  modifications have been applied in this version. The conflict in
  mptcp_pm_create_subflow_or_signal_addr() has been resolved by taking
  the newer version, which skip a lock if it is not needed. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>