CVE-2024-26663: NULL Pointer Dereference

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

tipc: Check the bearer type before calling tipc_udp_nl_bearer_add()

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().