CVE-2024-26663: tipc: Check the bearer type before calling tipc_udp_nl_bearer_add()

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

tipc: Check the bearer type before calling tipcudpnlbeareradd()

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:tipcudpisknownpeer+0x9c/0x250 net/tipc/udpmedia.c:291 ... Call Trace: <TASK> tipcudpnlbeareradd+0x212/0x2f0 net/tipc/udpmedia.c:646 tipcnlbeareradd+0x21e/0x360 net/tipc/bearer.c:1089 genlfamilyrcvmsgdoit+0x1fc/0x2e0 net/netlink/genetlink.c:972 genlfamilyrcvmsg net/netlink/genetlink.c:1052 [inline] genlrcvmsg+0x561/0x800 net/netlink/genetlink.c:1067 netlinkrcvskb+0x16b/0x440 net/netlink/afnetlink.c:2544 genlrcv+0x28/0x40 net/netlink/genetlink.c:1076 netlinkunicastkernel net/netlink/afnetlink.c:1341 [inline] netlinkunicast+0x53b/0x810 net/netlink/afnetlink.c:1367 netlinksendmsg+0x8b7/0xd70 net/netlink/afnetlink.c:1909 socksendmsgnosec net/socket.c:730 [inline] socksendmsg+0xd5/0x180 net/socket.c:745 syssendmsg+0x6ac/0x940 net/socket.c:2584 syssendmsg+0x135/0x1d0 net/socket.c:2638 syssendmsg+0x117/0x1e0 net/socket.c:2667 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x40/0x110 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

The cause of this issue is that when tipcnlbeareradd() is called with the TIPCNLABEARERUDPOPTS attribute, tipcudpnlbeareradd() is called even if the bearer is not UDP.

tipcudpisknownpeer() called by tipcudpnlbeareradd() assumes that the mediaptr field of the tipcbearer has an udpbearer type object, so the function goes crazy for non-UDP bearers.

This patch fixes the issue by checking the bearer type before calling tipcudpnlbeareradd() in tipcnlbeareradd().