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syzbot reported the following general protection fault [1]:

general protection fault, probably for non-canonical address 0xdffffc0000000010: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000080-0x0000000000000087]
...
RIP: 0010:tipc_udp_is_known_peer+0x9c/0x250 net/tipc/udp_media.c:291
...
Call Trace:
 <TASK>
 tipc_udp_nl_bearer_add+0x212/0x2f0 net/tipc/udp_media.c:646
 tipc_nl_bearer_add+0x21e/0x360 net/tipc/bearer.c:1089
 genl_family_rcv_msg_doit+0x1fc/0x2e0 net/netlink/genetlink.c:972
 genl_family_rcv_msg net/netlink/genetlink.c:1052 [inline]
 genl_rcv_msg+0x561/0x800 net/netlink/genetlink.c:1067
 netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2544
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1076
 netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
 netlink_unicast+0x53b/0x810 net/netlink/af_netlink.c:1367
 netlink_sendmsg+0x8b7/0xd70 net/netlink/af_netlink.c:1909
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0xd5/0x180 net/socket.c:745
 ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
 ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
 __sys_sendmsg+0x117/0x1e0 net/socket.c:2667
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

The cause of this issue is that when tipc_nl_bearer_add() is called with
the TIPC_NLA_BEARER_UDP_OPTS attribute, tipc_udp_nl_bearer_add() is called
even if the bearer is not UDP.

tipc_udp_is_known_peer() called by tipc_udp_nl_bearer_add() assumes that
the media_ptr field of the tipc_bearer has an udp_bearer type object, so
the function goes crazy for non-UDP bearers.

This patch fixes the issue by checking the bearer type before calling
tipc_udp_nl_bearer_add() in tipc_nl_bearer_add().

Fixes: ef20cd4d ("tipc: introduce UDP replicast")
Reported-and-tested-by: syzbot+5142b87a9abc510e14fa@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5142b87a9abc510e14fa

 [1]
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Tung Nguyen <tung.q.nguyen@dektech.com.au>
Link: https://lore.kernel.org/r/20240131152310.4089541-1-syoshida@redhat.com

Signed-off-by: Paolo Abeni <pabeni@redhat.com>