char: xillybus: Prevent use-after-free due to race condition

The driver for XillyUSB devices maintains a kref reference count on each
xillyusb_dev structure, which represents a physical device. This reference
count reaches zero when the device has been disconnected and there are no
open file descriptors that are related to the device. When this occurs,
kref_put() calls cleanup_dev(), which clears up the device's data,
including the structure itself.

However, when xillyusb_open() is called, this reference count becomes
tricky: This function needs to obtain the xillyusb_dev structure that
relates to the inode's major and minor (as there can be several such).
xillybus_find_inode() (which is defined in xillybus_class.c) is called
for this purpose. xillybus_find_inode() holds a mutex that is global in
xillybus_class.c to protect the list of devices, and releases this
mutex before returning. As a result, nothing protects the xillyusb_dev's
reference counter from being decremented to zero before xillyusb_open()
increments it on its own behalf. Hence the structure can be freed
due to a rare race condition.

To solve this, a mutex is added. It is locked by xillyusb_open() before
the call to xillybus_find_inode() and is released only after the kref
counter has been incremented on behalf of the newly opened inode. This
protects the kref reference counters of all xillyusb_dev structs from
being decremented by xillyusb_disconnect() during this time segment, as
the call to kref_put() in this function is done with the same lock held.

There is no need to hold the lock on other calls to kref_put(), because
if xillybus_find_inode() finds a struct, xillyusb_disconnect() has not
made the call to remove it, and hence not made its call to kref_put(),
which takes place afterwards. Hence preventing xillyusb_disconnect's
call to kref_put() is enough to ensure that the reference doesn't reach
zero before it's incremented by xillyusb_open().

It would have been more natural to increment the reference count in
xillybus_find_inode() of course, however this function is also called by
Xillybus' driver for PCIe / OF, which registers a completely different
structure. Therefore, xillybus_find_inode() treats these structures as
void pointers, and accordingly can't make any changes.

Reported-by: Hyunwoo Kim <imv4bel@gmail.com>
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://lore.kernel.org/r/20221030094209.65916-1-eli.billauer@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

char: xillybus: fix a refcount leak in cleanup_dev()

usb_get_dev is called in xillyusb_probe. So it is better to call
usb_put_dev before xdev is released.

Acked-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Link: https://lore.kernel.org/r/20220406075703.23464-1-hbh25y@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

char: xillybus: fix msg_ep UAF in xillyusb_probe()

When endpoint_alloc() return failed in xillyusb_setup_base_eps(),
'xdev->msg_ep' will be freed but not set to NULL. That lets program
enter fail handling to cleanup_dev() in xillyusb_probe(). Check for
'xdev->msg_ep' is invalid in cleanup_dev() because 'xdev->msg_ep' did
not set to NULL when was freed. So the UAF problem for 'xdev->msg_ep'
is triggered.

==================================================================
BUG: KASAN: use-after-free in fifo_mem_release+0x1f4/0x210
CPU: 0 PID: 166 Comm: kworker/0:2 Not tainted 5.15.0-rc5+ #19
Call Trace:
dump_stack_lvl+0xe2/0x152
print_address_description.constprop.0+0x21/0x140
? fifo_mem_release+0x1f4/0x210
kasan_report.cold+0x7f/0x11b
? xillyusb_probe+0x530/0x700
? fifo_mem_release+0x1f4/0x210
fifo_mem_release+0x1f4/0x210
? __sanitizer_cov_trace_pc+0x1d/0x50
endpoint_dealloc+0x35/0x2b0
cleanup_dev+0x90/0x120
xillyusb_probe+0x59a/0x700
...

Freed by task 166:
kasan_save_stack+0x1b/0x40
kasan_set_track+0x1c/0x30
kasan_set_free_info+0x20/0x30
__kasan_slab_free+0x109/0x140
kfree+0x117/0x4c0
xillyusb_probe+0x606/0x700

Set 'xdev->msg_ep' to NULL after being freed in xillyusb_setup_base_eps()
to fix the UAF problem.

Fixes: a53d1202aef1 ("char: xillybus: Add driver for XillyUSB (Xillybus variant for USB)")
Cc: stable <stable@vger.kernel.org>
Acked-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Link: https://lore.kernel.org/r/20211016052047.1611983-1-william.xuanziyang@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

char: xillybus: Fix spelling mistake "overflew" -> "overflowed"

There is a spelling mistake in a dev_err message. Fix it.

Acked-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210601102201.8489-1-colin.king@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

char: xillybus: Remove unneeded MODULE_VERSION() usage

MODULE_VERSION is useless for in-kernel drivers, so these are removed from
files in drivers/char/xillybus/

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://lore.kernel.org/r/20210528092242.51104-2-eli.billauer@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

char: xillybus: Add driver for XillyUSB (Xillybus variant for USB)

The XillyUSB driver is the USB variant for the Xillybus FPGA IP core.
Even though it presents a nearly identical API on the FPGA and host,
it's almost a complete rewrite of the driver: The framework for exchanging
data on a USB bus is fundamentally different from doing the same with a
PCIe interface, which leaves very little in common between the existing
driver and the new one for XillyUSB.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://lore.kernel.org/r/20210526100311.56327-3-eli.billauer@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>