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

tipc: fix kernel panic when enabling bearer

When enabling a bearer on a node, a kernel panic is observed:

[    4.498085] RIP: 0010:tipc_mon_prep+0x4e/0x130 [tipc]
...
[    4.520030] Call Trace:
[    4.520689]  <IRQ>
[    4.521236]  tipc_link_build_proto_msg+0x375/0x750 [tipc]
[    4.522654]  tipc_link_build_state_msg+0x48/0xc0 [tipc]
[    4.524034]  __tipc_node_link_up+0xd7/0x290 [tipc]
[    4.525292]  tipc_rcv+0x5da/0x730 [tipc]
[    4.526346]  ? __netif_receive_skb_core+0xb7/0xfc0
[    4.527601]  tipc_l2_rcv_msg+0x5e/0x90 [tipc]
[    4.528737]  __netif_receive_skb_list_core+0x20b/0x260
[    4.530068]  netif_receive_skb_list_internal+0x1bf/0x2e0
[    4.531450]  ? dev_gro_receive+0x4c2/0x680
[    4.532512]  napi_complete_done+0x6f/0x180
[    4.533570]  virtnet_poll+0x29c/0x42e [virtio_net]
...

The node in question is receiving activate messages in another
thread after changing bearer status to allow message sending/
receiving in current thread:

         thread 1           |              thread 2
         --------           |              --------
                            |
tipc_enable_bearer()        |
  test_and_set_bit_lock()   |
    tipc_bearer_xmit_skb()  |
                            | tipc_l2_rcv_msg()
                            |   tipc_rcv()
                            |     __tipc_node_link_up()
                            |       tipc_link_build_state_msg()
                            |         tipc_link_build_proto_msg()
                            |           tipc_mon_prep()
                            |           {
                            |             ...
                            |             // null-pointer dereference
                            |             u16 gen = mon->dom_gen;
                            |             ...
                            |           }
  // Not being executed yet |
  tipc_mon_create()         |
  {                         |
    ...                     |
    // allocate             |
    mon = kzalloc();        |
    ...                     |
  }                         |

Monitoring pointer in thread 2 is dereferenced before monitoring data
is allocated in thread 1. This causes kernel panic.

This commit fixes it by allocating the monitoring data before enabling
the bearer to receive messages.

kernel.org https://git.kernel.org/stable/c/2de76d37d4a6dca9b96ea51da24d4290e6cfa1a5 [No types assigned]

kernel.org https://git.kernel.org/stable/c/be4977b847f5d5cedb64d50eaaf2218c3a55a3a3 [No types assigned]

kernel.org https://git.kernel.org/stable/c/f4f59fdbc748805b08c13dae14c01f0518c77c94 [No types assigned]

kernel.org https://git.kernel.org/stable/c/f96dc3adb9a97b8f3dfdb88796483491a3006b71 [No types assigned]