tipc: read le->link under the node lock in tipc_node_link_down()

Summary

In the Linux kernel, the following vulnerability has been resolved: tipc: read le->link under the node lock in tipc_node_link_down() tipc_node_link_down() caches the link pointer before taking n->lock: struct tipc_link l = le->link; / unlocked */ if (!l) return; tipc_node_write_lock(n); if (!tipc_link_is_establishing(l)) { /* deref l */ ... tipc_link_reset(l); /* write into l */ if (delete) { kfree(l); le->link = NULL; The delete=true caller frees that very object under n->lock, so the lock does not protect the cached pointer against it: • CPU A, delete=false: tipc_rcv() on TIPC_LINK_DOWN_EVT, or the link supervision timer via tipc_node_timeout(), reads l unlocked and then dereferences it under n->lock; • CPU B, delete=true: netlink TIPC_NL_BEARER_DISABLE -> bearer_disable() -> tipc_node_delete_links() -> tipc_node_link_down(n, bearer_id, true) -> kfree(l). The link is freed with plain kfree(), not kfree_rcu(), and for UDP bearers disable_media() only schedules the asynchronous cleanup_bearer() work, so its synchronize_net() runs after the links are already gone. An in-flight CPU A that has read l therefore dereferences freed memory once B frees it: a use-after-free read in tipc_link_is_establishing(), and a use-after-free write via tipc_link_reset() on the establishing branch. The following trace was captured on 7.2.0-rc5-00284-gaf39eb111ce6: BUG: KASAN: slab-use-after-free in tipc_link_is_establishing (net/tipc/link.c:285) Read of size 4 at addr ffff88802e2aa068 by task swapper/2/0 tipc_link_is_establishing (net/tipc/link.c:285) tipc_node_link_down (net/tipc/node.c:1076) tipc_node_timeout (net/tipc/node.c:843) Allocated by task 9549: tipc_link_create (net/tipc/link.c:490) tipc_node_check_dest (net/tipc/node.c:1279) tipc_disc_rcv (net/tipc/discover.c:252) tipc_udp_recv (net/tipc/udp_media.c:389) Freed by task 9549: tipc_node_link_down (net/tipc/node.c:1084) tipc_node_delete_links (net/tipc/node.c:1320) bearer_disable (net/tipc/bearer.c:414) __tipc_nl_bearer_disable (net/tipc/bearer.c:992) Move the le->link read inside tipc_node_write_lock(), so it is serialised against the kfree() in the delete path. A racing teardown now either has not run yet, and we see a valid link, or has already run, and we see NULL.

Timeline

1. Aug 22, 2026, 3:31 PM UTCCVE published
2. Oct 16, 2026, 7:02 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 16, 2026, 7:06 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in 2be741ad565c610871a6a95062c12c39da7168fd; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in 69d209461c110388710e483a130caf051e4fd09a; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in de017c22135f545ca4e65d1eada22887b64958eb; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in 47ba70891b10b2feb52462086b7fcd2ad75d3ce3; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in a714d62513befef37f71f4ae89bb1fe173b65f2e; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in c3f2347a47754eac690967cfd82cb6d559817b07; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in 5558a8312452ddb21eff22b1cbd84302ad951944; From 73f646cec35477b5099d7e952297cb9e1855be45 · fixed in cba9ccb47e9fa4cc77692fb896cc5ab57a667882

• Linux Linux

  4.4

• KernelLinux

  From 4.4.0 · fixed in 5.10.265; From 5.11.0 · fixed in 5.15.216; From 5.16.0 · fixed in 6.1.183; From 6.2.0 · fixed in 6.6.152; From 6.7.0 · fixed in 6.12.104; From 6.13.0 · fixed in 6.18.45; From 6.19.0 · fixed in 7.1.9

References 8