{"id":"CVE-2026-45866","summary":"serial: caif: fix use-after-free in caif_serial ldisc_close()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nserial: caif: fix use-after-free in caif_serial ldisc_close()\n\nThere is a use-after-free bug in caif_serial where handle_tx() may\naccess ser-\u003etty after the tty has been freed.\n\nThe race condition occurs between ldisc_close() and packet transmission:\n\n    CPU 0 (close)                     CPU 1 (xmit)\n    -------------                     ------------\n    ldisc_close()\n      tty_kref_put(ser-\u003etty)\n      [tty may be freed here]\n                     \u003c-- race window --\u003e\n                                      caif_xmit()\n                                        handle_tx()\n                                          tty = ser-\u003etty  // dangling ptr\n                                          tty-\u003eops-\u003ewrite() // UAF!\n      schedule_work()\n        ser_release()\n          unregister_netdevice()\n\nThe root cause is that tty_kref_put() is called in ldisc_close() while\nthe network device is still active and can receive packets.\n\nSince ser and tty have a 1:1 binding relationship with consistent\nlifecycles (ser is allocated in ldisc_open and freed in ser_release\nvia unregister_netdevice, and each ser binds exactly one tty), we can\nsafely defer the tty reference release to ser_release() where the\nnetwork device is unregistered.\n\nFix this by moving tty_kref_put() from ldisc_close() to ser_release(),\nafter unregister_netdevice(). This ensures the tty reference is held\nas long as the network device exists, preventing the UAF.\n\nNote: We save ser-\u003etty before unregister_netdevice() because ser is\nembedded in netdev's private data and will be freed along with netdev\n(needs_free_netdev = true).\n\nHow to reproduce: Add mdelay(500) at the beginning of ldisc_close()\nto widen the race window, then run the reproducer program [1].\n\nNote: There is a separate deadloop issue in handle_tx() when using\nPORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper\nserial backend). This deadloop exists even without this patch,\nand is likely caused by inconsistency between uart_write_room() and\nuart_write() in serial core. It has been addressed in a separate\npatch [2].\n\nKASAN report:\n\n==================================================================\nBUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620\nRead of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929\n\nCall Trace:\n \u003cTASK\u003e\n dump_stack_lvl+0x10e/0x1f0\n print_report+0xd0/0x630\n kasan_report+0xe4/0x120\n handle_tx+0x5d1/0x620\n dev_hard_start_xmit+0x9d/0x6c0\n __dev_queue_xmit+0x6e2/0x4410\n packet_xmit+0x243/0x360\n packet_sendmsg+0x26cf/0x5500\n __sys_sendto+0x4a3/0x520\n __x64_sys_sendto+0xe0/0x1c0\n do_syscall_64+0xc9/0xf80\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\nRIP: 0033:0x7f615df2c0d7\n\nAllocated by task 9930:\n\nFreed by task 64:\n\nLast potentially related work creation:\n\nThe buggy address belongs to the object at ffff8881131e1000\n which belongs to the cache kmalloc-cg-2k of size 2048\nThe buggy address is located 1168 bytes inside of\n freed 2048-byte region [ffff8881131e1000, ffff8881131e1800)\n\nThe buggy address belongs to the physical page:\npage_owner tracks the page as allocated\npage last free pid 9778 tgid 9778 stack trace:\n\nMemory state around the buggy address:\n ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb\n ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb\n\u003effff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb\n                         ^\n ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb\n ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb\n==================================================================\n[1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb\n[2]: https://lore.kernel.org/linux-serial/20260204074327.226165-1-jiayuan.chen@linux.dev/T/#u","modified":"2026-06-27T11:55:13.422786851Z","published":"2026-05-27T12:15:46.135Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45866.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/308e7e4d0a846359685f40aade023aee7b27284c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/331e2b7051635780edea248dd08ae2026c126f4a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/40962f2bf8cdba63af23aec95ad3f49b689e58e2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4e63d6f68544ae5269ac9735ae5b69b59b5b8725"},{"type":"WEB","url":"https://git.kernel.org/stable/c/52731ef4438155cea782fac74e547a327ab9e7c5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5e266ba8d330d3b8e5bc198f238cd8901826cfa1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c8c197aaa56b25a2d54f3aa07e27e228d6c08546"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d3c75db4e0460641dbcd274b40867e252d801da1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45866.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45866"},{"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":"56e0ef527b184b3de2d7f88c6190812b2b2ac6bf"},{"fixed":"5e266ba8d330d3b8e5bc198f238cd8901826cfa1"},{"fixed":"d3c75db4e0460641dbcd274b40867e252d801da1"},{"fixed":"4e63d6f68544ae5269ac9735ae5b69b59b5b8725"},{"fixed":"331e2b7051635780edea248dd08ae2026c126f4a"},{"fixed":"52731ef4438155cea782fac74e547a327ab9e7c5"},{"fixed":"c8c197aaa56b25a2d54f3aa07e27e228d6c08546"},{"fixed":"40962f2bf8cdba63af23aec95ad3f49b689e58e2"},{"fixed":"308e7e4d0a846359685f40aade023aee7b27284c"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-45866.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.11.0"},{"fixed":"5.10.252"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.202"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.165"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.128"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.75"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.14"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-45866.json"}}],"schema_version":"1.7.5"}