Commit f6c7bc4a authored by Kuen-Han Tsai's avatar Kuen-Han Tsai Committed by Greg Kroah-Hartman
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Revert "usb: gadget: u_serial: Add null pointer check in gs_start_io" 



This reverts commit ffd603f2.

Commit ffd603f2 ("usb: gadget: u_serial: Add null pointer check in
gs_start_io") adds null pointer checks at the beginning of the
gs_start_io() function to prevent a null pointer dereference. However,
these checks are redundant because the function's comment already
requires callers to hold the port_lock and ensure port.tty and port_usb
are not null. All existing callers already follow these rules.

The true cause of the null pointer dereference is a race condition. When
gs_start_io() calls either gs_start_rx() or gs_start_tx(), the port_lock
is temporarily released for usb_ep_queue(). This allows port.tty and
port_usb to be cleared.

Fixes: ffd603f2 ("usb: gadget: u_serial: Add null pointer check in gs_start_io")
Cc: stable <stable@kernel.org>
Signed-off-by: default avatarKuen-Han Tsai <khtsai@google.com>
Reviewed-by: default avatarPrashanth K <prashanth.k@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250617050844.1848232-1-khtsai@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 31a6afbe

drivers/usb/gadget/function/u_serial.c

+1 −5
Original line number Diff line number Diff line
@@ -544,20 +544,16 @@ static int gs_alloc_requests(struct usb_ep *ep, struct list_head *head, 
static int gs_start_io(struct gs_port *port)

{

	struct list_head	*head = &port->read_pool;

	struct usb_ep		*ep;

	struct usb_ep		*ep = port->port_usb->out;

	int			status;

	unsigned		started;



	if (!port->port_usb || !port->port.tty)

		return -EIO;



	/* Allocate RX and TX I/O buffers.  We can't easily do this much

	 * earlier (with GFP_KERNEL) because the requests are coupled to

	 * endpoints, as are the packet sizes we'll be using.  Different

	 * configurations may use different endpoints with a given port;

	 * and high speed vs full speed changes packet sizes too.

	 */

	ep = port->port_usb->out;

	status = gs_alloc_requests(ep, head, gs_read_complete,

		&port->read_allocated);

	if (status)