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commit cfd6f1a7b42f62523c96d9703ef32b0dbc495ba4 upstream. A race condition occurs when ffs_func_eps_enable() runs concurrently with ffs_data_reset(). The ffs_data_clear() called in ffs_data_reset() sets ffs->epfiles to NULL before resetting ffs->eps_count to 0, leading to a NULL pointer dereference when accessing epfile->ep in ffs_func_eps_enable() after successful usb_ep_enable(). The ffs->epfiles pointer is set to NULL in both ffs_data_clear() and ffs_data_close() functions, and its modification is protected by the spinlock ffs->eps_lock. And the whole ffs_func_eps_enable() function is also protected by ffs->eps_lock. Thus, add NULL pointer handling for ffs->epfiles in the ffs_func_eps_enable() function to fix issues Signed-off-by: Owen Gu <guhuinan@xiaomi.com> Link: https://lore.kernel.org/r/20250915092907.17802-1-guhuinan@xiaomi.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Ulrich Hecht <uli@kernel.org>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("hub_wq").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.