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.
Duoming Zhou
authored
There are race conditions that may lead to UAF bugs in ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(), ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we call ax25_release() to deallocate ax25_dev. One of the UAF bugs caused by ax25_release() is shown below: (Thread 1) | (Thread 2) ax25_dev_device_up() //(1) | ... | ax25_kill_by_device() ax25_bind() //(2) | ax25_connect() | ... ax25_std_establish_data_link() | ax25_start_t1timer() | ax25_dev_device_down() //(3) mod_timer(&ax25->t1timer,..) | | ax25_release() (wait a time) | ... | ax25_dev_put(ax25_dev) //(4)FREE ax25_t1timer_expiry() | ax25->ax25_dev->values[..] //USE| ... ... | We increase the refcount of ax25_dev in position (1) and (2), and decrease the refcount of ax25_dev in position (3) and (4). The ax25_dev will be freed in position (4) and be used in ax25_t1timer_expiry(). The fail log is shown below: ============================================================== [ 106.116942] BUG: KASAN: use-after-free in ax25_t1timer_expiry+0x1c/0x60 [ 106.116942] Read of size 8 at addr ffff88800bda9028 by task swapper/0/0 [ 106.116942] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-06123-g0905eec574 [ 106.116942] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-14 [ 106.116942] Call Trace: ... [ 106.116942] ax25_t1timer_expiry+0x1c/0x60 [ 106.116942] call_timer_fn+0x122/0x3d0 [ 106.116942] __run_timers.part.0+0x3f6/0x520 [ 106.116942] run_timer_softirq+0x4f/0xb0 [ 106.116942] __do_softirq+0x1c2/0x651 ... This patch adds del_timer_sync() in ax25_release(), which could ensure that all timers stop before we deallocate ax25_dev. Signed-off-by:Duoming Zhou <duoming@zju.edu.cn> Signed-off-by:
Paolo Abeni <pabeni@redhat.com>
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