GHSA-9834-966G-Q77H
Vulnerability from github – Published: 2026-05-27 15:33 – Updated: 2026-05-27 15:33In the Linux kernel, the following vulnerability has been resolved:
serial: caif: fix use-after-free in caif_serial ldisc_close()
There is a use-after-free bug in caif_serial where handle_tx() may access ser->tty after the tty has been freed.
The race condition occurs between ldisc_close() and packet transmission:
CPU 0 (close) CPU 1 (xmit)
------------- ------------
ldisc_close()
tty_kref_put(ser->tty)
[tty may be freed here]
<-- race window -->
caif_xmit()
handle_tx()
tty = ser->tty // dangling ptr
tty->ops->write() // UAF!
schedule_work()
ser_release()
unregister_netdevice()
The root cause is that tty_kref_put() is called in ldisc_close() while the network device is still active and can receive packets.
Since ser and tty have a 1:1 binding relationship with consistent lifecycles (ser is allocated in ldisc_open and freed in ser_release via unregister_netdevice, and each ser binds exactly one tty), we can safely defer the tty reference release to ser_release() where the network device is unregistered.
Fix this by moving tty_kref_put() from ldisc_close() to ser_release(), after unregister_netdevice(). This ensures the tty reference is held as long as the network device exists, preventing the UAF.
Note: We save ser->tty before unregister_netdevice() because ser is embedded in netdev's private data and will be freed along with netdev (needs_free_netdev = true).
How to reproduce: Add mdelay(500) at the beginning of ldisc_close() to widen the race window, then run the reproducer program 1.
Note: There is a separate deadloop issue in handle_tx() when using PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper serial backend). This deadloop exists even without this patch, and is likely caused by inconsistency between uart_write_room() and uart_write() in serial core. It has been addressed in a separate patch 2.
KASAN report:
================================================================== BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620 Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929
Call Trace: dump_stack_lvl+0x10e/0x1f0 print_report+0xd0/0x630 kasan_report+0xe4/0x120 handle_tx+0x5d1/0x620 dev_hard_start_xmit+0x9d/0x6c0 __dev_queue_xmit+0x6e2/0x4410 packet_xmit+0x243/0x360 packet_sendmsg+0x26cf/0x5500 __sys_sendto+0x4a3/0x520 __x64_sys_sendto+0xe0/0x1c0 do_syscall_64+0xc9/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f615df2c0d7
Allocated by task 9930:
Freed by task 64:
Last potentially related work creation:
The buggy address belongs to the object at ffff8881131e1000 which belongs to the cache kmalloc-cg-2k of size 2048 The buggy address is located 1168 bytes inside of freed 2048-byte region [ffff8881131e1000, ffff8881131e1800)
The buggy address belongs to the physical page: page_owner tracks the page as allocated page last free pid 9778 tgid 9778 stack trace:
Memory state around the buggy address: ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================
{
"affected": [],
"aliases": [
"CVE-2026-45866"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-27T14:16:58Z",
"severity": null
},
"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\u0027s 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",
"id": "GHSA-9834-966g-q77h",
"modified": "2026-05-27T15:33:13Z",
"published": "2026-05-27T15:33:13Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45866"
},
{
"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"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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|---|
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