9ded5ae40f
[ Upstream commit ef27324e2cb7bb24542d6cb2571740eefe6b00dc ]
Our detector found a concurrent use-after-free bug when detaching an
NCI device. The main reason for this bug is the unexpected scheduling
between the used delayed mechanism (timer and workqueue).
The race can be demonstrated below:
Thread-1 Thread-2
| nci_dev_up()
| nci_open_device()
| __nci_request(nci_reset_req)
| nci_send_cmd
| queue_work(cmd_work)
nci_unregister_device() |
nci_close_device() | ...
del_timer_sync(cmd_timer)[1] |
... | Worker
nci_free_device() | nci_cmd_work()
kfree(ndev)[3] | mod_timer(cmd_timer)[2]
In short, the cleanup routine thought that the cmd_timer has already
been detached by [1] but the mod_timer can re-attach the timer [2], even
it is already released [3], resulting in UAF.
This UAF is easy to trigger, crash trace by POC is like below
[ 66.703713] ==================================================================
[ 66.703974] BUG: KASAN: use-after-free in enqueue_timer+0x448/0x490
[ 66.703974] Write of size 8 at addr ffff888009fb7058 by task kworker/u4:1/33
[ 66.703974]
[ 66.703974] CPU: 1 PID: 33 Comm: kworker/u4:1 Not tainted 5.18.0-rc2 #5
[ 66.703974] Workqueue: nfc2_nci_cmd_wq nci_cmd_work
[ 66.703974] Call Trace:
[ 66.703974] <TASK>
[ 66.703974] dump_stack_lvl+0x57/0x7d
[ 66.703974] print_report.cold+0x5e/0x5db
[ 66.703974] ? enqueue_timer+0x448/0x490
[ 66.703974] kasan_report+0xbe/0x1c0
[ 66.703974] ? enqueue_timer+0x448/0x490
[ 66.703974] enqueue_timer+0x448/0x490
[ 66.703974] __mod_timer+0x5e6/0xb80
[ 66.703974] ? mark_held_locks+0x9e/0xe0
[ 66.703974] ? try_to_del_timer_sync+0xf0/0xf0
[ 66.703974] ? lockdep_hardirqs_on_prepare+0x17b/0x410
[ 66.703974] ? queue_work_on+0x61/0x80
[ 66.703974] ? lockdep_hardirqs_on+0xbf/0x130
[ 66.703974] process_one_work+0x8bb/0x1510
[ 66.703974] ? lockdep_hardirqs_on_prepare+0x410/0x410
[ 66.703974] ? pwq_dec_nr_in_flight+0x230/0x230
[ 66.703974] ? rwlock_bug.part.0+0x90/0x90
[ 66.703974] ? _raw_spin_lock_irq+0x41/0x50
[ 66.703974] worker_thread+0x575/0x1190
[ 66.703974] ? process_one_work+0x1510/0x1510
[ 66.703974] kthread+0x2a0/0x340
[ 66.703974] ? kthread_complete_and_exit+0x20/0x20
[ 66.703974] ret_from_fork+0x22/0x30
[ 66.703974] </TASK>
[ 66.703974]
[ 66.703974] Allocated by task 267:
[ 66.703974] kasan_save_stack+0x1e/0x40
[ 66.703974] __kasan_kmalloc+0x81/0xa0
[ 66.703974] nci_allocate_device+0xd3/0x390
[ 66.703974] nfcmrvl_nci_register_dev+0x183/0x2c0
[ 66.703974] nfcmrvl_nci_uart_open+0xf2/0x1dd
[ 66.703974] nci_uart_tty_ioctl+0x2c3/0x4a0
[ 66.703974] tty_ioctl+0x764/0x1310
[ 66.703974] __x64_sys_ioctl+0x122/0x190
[ 66.703974] do_syscall_64+0x3b/0x90
[ 66.703974] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 66.703974]
[ 66.703974] Freed by task 406:
[ 66.703974] kasan_save_stack+0x1e/0x40
[ 66.703974] kasan_set_track+0x21/0x30
[ 66.703974] kasan_set_free_info+0x20/0x30
[ 66.703974] __kasan_slab_free+0x108/0x170
[ 66.703974] kfree+0xb0/0x330
[ 66.703974] nfcmrvl_nci_unregister_dev+0x90/0xd0
[ 66.703974] nci_uart_tty_close+0xdf/0x180
[ 66.703974] tty_ldisc_kill+0x73/0x110
[ 66.703974] tty_ldisc_hangup+0x281/0x5b0
[ 66.703974] __tty_hangup.part.0+0x431/0x890
[ 66.703974] tty_release+0x3a8/0xc80
[ 66.703974] __fput+0x1f0/0x8c0
[ 66.703974] task_work_run+0xc9/0x170
[ 66.703974] exit_to_user_mode_prepare+0x194/0x1a0
[ 66.703974] syscall_exit_to_user_mode+0x19/0x50
[ 66.703974] do_syscall_64+0x48/0x90
[ 66.703974] entry_SYSCALL_64_after_hwframe+0x44/0xae
To fix the UAF, this patch adds flush_workqueue() to ensure the
nci_cmd_work is finished before the following del_timer_sync.
This combination will promise the timer is actually detached.
Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.