CVE-2026-64543tipc: fix use-after-free of the discoverer in tipc_disc_rcv()

Official description

In the Linux kernel, the following vulnerability has been resolved: tipc: fix use-after-free of the discoverer in tipc_disc_rcv() bearer_disable() frees b->disc with tipc_disc_delete()'s plain kfree(), but tipc_disc_rcv() still dereferences b->disc in RX softirq under rcu_read_lock() (tipc_udp_recv -> tipc_rcv -> tipc_disc_rcv). L2 bearers are safe thanks to the synchronize_net() in tipc_disable_l2_media(), but the UDP bearer defers that call to the cleanup_bearer() workqueue, so the discoverer is freed with no grace period: BUG: KASAN: slab-use-after-free in tipc_disc_rcv (net/tipc/discover.c:149) Read of size 8 at addr ffff88802348b728 by task poc_tipc/184 <IRQ> tipc_disc_rcv (net/tipc/discover.c:149) tipc_rcv (net/tipc/node.c:2126) tipc_udp_recv (net/tipc/udp_media.c:391) udp_rcv (net/ipv4/udp.c:2643) ip_local_deliver_finish (net/ipv4/ip_input.c:241) </IRQ> Freed by task 181: kfree (mm/slub.c:6565) bearer_disable (net/tipc/bearer.c:418) tipc_nl_bearer_disable (net/tipc/bearer.c:1001) The bearer is freed with kfree_rcu(); free the discoverer the same way. Add an rcu_head to struct tipc_discoverer and free it and its skb from an RCU callback. Because the RCU callback (tipc_disc_free_rcu) lives in module text, a call_rcu() that is still pending when the tipc module is unloaded would invoke a freed function. Add an rcu_barrier() to tipc_exit() after the bearer subsystem has been torn down, so all pending discoverer callbacks have run before the module text goes away. Reachable from an unprivileged user namespace: the TIPCv2 genl family is netnsok and its bearer commands have no GENL_ADMIN_PERM. Needs CONFIG_TIPC and CONFIG_TIPC_MEDIA_UDP.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/380413cdfd29fb9fa486c82889132b680c4983c5
• https://git.kernel.org/stable/c/f05b3f4c78370469286879c765f5a1dd39dbcd32
• https://git.kernel.org/stable/c/4da2ac7749411971e1b222b992da5a172ce45f98
• https://git.kernel.org/stable/c/5e215bf1c47fdddf8203a0fe80a0ed594065f101
• https://git.kernel.org/stable/c/ec7d54d8cc1723921d671e3272b427c96366506f
• https://git.kernel.org/stable/c/a0c5fdeb5fa257f8c6d469af266bc087cb5de6a2
• https://git.kernel.org/stable/c/b65289e1c3f352a9f92c6e19713ddd647e033253
• https://git.kernel.org/stable/c/1579342d71133da7f00daa02c75cebec7372097b