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

JIRA: https://issues.redhat.com/browse/RHEL-115652
Tested: compile only

commit f82727a
Author: Haixia Qu <hxqu@hillstonenet.com>
Date:   Tue Jun 17 05:56:24 2025 +0000

    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.

    Fixes: 832629c ("tipc: add UDP remoteip dump to netlink API")
    Signed-off-by: Haixia Qu <hxqu@hillstonenet.com>
    Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
    Link: https://patch.msgid.link/20250617055624.2680-1-hxqu@hillstonenet.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Xin Long <lxin@redhat.com>

Author: Xin Long

net/tipc/udp_media.c

@@ -489,7 +489,7 @@ int tipc_udp_nl_dump_remoteip(struct sk_buff *skb, struct netlink_callback *cb)
 
 		rtnl_lock();
 		b = tipc_bearer_find(net, bname);
-		if (!b) {
+		if (!b || b->bcast_addr.media_id != TIPC_MEDIA_TYPE_UDP) {
 			rtnl_unlock();
 			return -EINVAL;
 		}
@@ -500,7 +500,7 @@ int tipc_udp_nl_dump_remoteip(struct sk_buff *skb, struct netlink_callback *cb)
 
 		rtnl_lock();
 		b = rtnl_dereference(tn->bearer_list[bid]);
-		if (!b) {
+		if (!b || b->bcast_addr.media_id != TIPC_MEDIA_TYPE_UDP) {
 			rtnl_unlock();
 			return -EINVAL;
 		}