tipc: fix null-ptr-deref when acquiring remote ip of ethernet bearer

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

tipc: fix null-ptr-deref when acquiring remote ip of ethernet bearer

The reproduction steps: 1. create a tun interface 2. enable l2 bearer 3. TIPC_NL_UDP_GET_REMOTEIP with media name set to tun

tipc: Started in network mode tipc: Node identity 8af312d38a21, cluster identity 4711 tipc: Enabled bearer <eth:syz_tun>, priority 1 Oops: general protection fault KASAN: null-ptr-deref in range CPU: 1 UID: 1000 PID: 559 Comm: poc Not tainted 6.16.0-rc1+ #117 PREEMPT Hardware name: QEMU Ubuntu 24.04 PC RIP: 0010:tipc_udp_nl_dump_remoteip+0x4a4/0x8f0

the ub was in fact a struct dev.

when bid != 0 && skip_cnt != 0, bearer_list[bid] may be NULL or other media when other thread changes it.

fix this by checking media_id.