6.15-stable review patch. If anyone has any objections, please let me know.
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From: Kuen-Han Tsai khtsai@google.com
commit f6c7bc4a6823a0a959f40866a1efe99bd03c2c5b upstream.
This reverts commit ffd603f214237e250271162a5b325c6199a65382.
Commit ffd603f21423 ("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: ffd603f21423 ("usb: gadget: u_serial: Add null pointer check in gs_start_io") Cc: stable stable@kernel.org Signed-off-by: Kuen-Han Tsai khtsai@google.com Reviewed-by: Prashanth K prashanth.k@oss.qualcomm.com Link: https://lore.kernel.org/r/20250617050844.1848232-1-khtsai@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/function/u_serial.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
--- a/drivers/usb/gadget/function/u_serial.c +++ b/drivers/usb/gadget/function/u_serial.c @@ -544,20 +544,16 @@ static int gs_alloc_requests(struct usb_ 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)