{"id":"CVE-2026-74609","summary":"tipc: read le-\u003elink under the node lock in tipc_node_link_down()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: read le-\u003elink under the node lock in tipc_node_link_down()\n\ntipc_node_link_down() caches the link pointer before taking n-\u003elock:\n\n\tstruct tipc_link *l = le-\u003elink;\t\t/* unlocked */\n\n\tif (!l)\n\t\treturn;\n\ttipc_node_write_lock(n);\n\tif (!tipc_link_is_establishing(l)) {\t/* deref l */\n\t...\n\t\ttipc_link_reset(l);\t\t/* write into l */\n\tif (delete) {\n\t\tkfree(l);\n\t\tle-\u003elink = NULL;\n\nThe delete=true caller frees that very object under n-\u003elock, so the lock\ndoes not protect the cached pointer against it:\n\n - CPU A, delete=false: tipc_rcv() on TIPC_LINK_DOWN_EVT, or the link\n   supervision timer via tipc_node_timeout(), reads l unlocked and then\n   dereferences it under n-\u003elock;\n - CPU B, delete=true: netlink TIPC_NL_BEARER_DISABLE -\u003e bearer_disable()\n   -\u003e tipc_node_delete_links() -\u003e tipc_node_link_down(n, bearer_id, true)\n   -\u003e kfree(l).\n\nThe link is freed with plain kfree(), not kfree_rcu(), and for UDP bearers\ndisable_media() only schedules the asynchronous cleanup_bearer() work, so\nits synchronize_net() runs after the links are already gone.  An in-flight\nCPU A that has read l therefore dereferences freed memory once B frees it:\na use-after-free read in tipc_link_is_establishing(), and a use-after-free\nwrite via tipc_link_reset() on the establishing branch.\n\nThe following trace was captured on 7.2.0-rc5-00284-gaf39eb111ce6:\n\n  BUG: KASAN: slab-use-after-free in tipc_link_is_establishing (net/tipc/link.c:285)\n  Read of size 4 at addr ffff88802e2aa068 by task swapper/2/0\n   tipc_link_is_establishing (net/tipc/link.c:285)\n   tipc_node_link_down (net/tipc/node.c:1076)\n   tipc_node_timeout (net/tipc/node.c:843)\n  Allocated by task 9549:\n   tipc_link_create (net/tipc/link.c:490)\n   tipc_node_check_dest (net/tipc/node.c:1279)\n   tipc_disc_rcv (net/tipc/discover.c:252)\n   tipc_udp_recv (net/tipc/udp_media.c:389)\n  Freed by task 9549:\n   tipc_node_link_down (net/tipc/node.c:1084)\n   tipc_node_delete_links (net/tipc/node.c:1320)\n   bearer_disable (net/tipc/bearer.c:414)\n   __tipc_nl_bearer_disable (net/tipc/bearer.c:992)\n\nMove the le-\u003elink read inside tipc_node_write_lock(), so it is serialised\nagainst the kfree() in the delete path.  A racing teardown now either has\nnot run yet, and we see a valid link, or has already run, and we see NULL.","modified":"2026-08-24T11:47:08.978296006Z","published":"2026-08-22T15:31:56.054Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74609.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2be741ad565c610871a6a95062c12c39da7168fd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/47ba70891b10b2feb52462086b7fcd2ad75d3ce3"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5558a8312452ddb21eff22b1cbd84302ad951944"},{"type":"WEB","url":"https://git.kernel.org/stable/c/69d209461c110388710e483a130caf051e4fd09a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a714d62513befef37f71f4ae89bb1fe173b65f2e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c3f2347a47754eac690967cfd82cb6d559817b07"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cba9ccb47e9fa4cc77692fb896cc5ab57a667882"},{"type":"WEB","url":"https://git.kernel.org/stable/c/de017c22135f545ca4e65d1eada22887b64958eb"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74609.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74609"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"73f646cec35477b5099d7e952297cb9e1855be45"},{"fixed":"2be741ad565c610871a6a95062c12c39da7168fd"},{"fixed":"69d209461c110388710e483a130caf051e4fd09a"},{"fixed":"de017c22135f545ca4e65d1eada22887b64958eb"},{"fixed":"47ba70891b10b2feb52462086b7fcd2ad75d3ce3"},{"fixed":"a714d62513befef37f71f4ae89bb1fe173b65f2e"},{"fixed":"c3f2347a47754eac690967cfd82cb6d559817b07"},{"fixed":"5558a8312452ddb21eff22b1cbd84302ad951944"},{"fixed":"cba9ccb47e9fa4cc77692fb896cc5ab57a667882"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74609.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.4.0"},{"fixed":"5.10.265"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.216"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.183"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.152"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.104"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.45"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74609.json"}}],"schema_version":"1.9.0"}