usb: gadget: u_serial: Fix race condition in TTY wakeup

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: u_serial: Fix race condition in TTY wakeup A race condition occurs when gs_start_io() calls either gs_start_rx() or gs_start_tx(), as those functions briefly drop the port_lock for usb_ep_queue(). This allows gs_close() and gserial_disconnect() to clear port.tty and port_usb, respectively. Use the null-safe TTY Port helper function to wake up TTY. Example CPU1: CPU2: gserial_connect() // lock gs_close() // await lock gs_start_rx() // unlock usb_ep_queue() gs_close() // lock, reset port.tty and unlock gs_start_rx() // lock tty_wakeup() // NPE

References

• https://git.kernel.org/stable/c/18d58a467ccf011078352d91b4d6a0108c7318e8
• https://git.kernel.org/stable/c/d43657b59f36e88289a6066f15bc9a80df5014eb
• https://git.kernel.org/stable/c/a5012673d49788f16bb4e375b002d7743eb642d9
• https://git.kernel.org/stable/c/ee8d688e2ba558f3bb8ac225113740be5f335417
• https://git.kernel.org/stable/c/c6eb4a05af3d0ba3bc4e8159287722fb9abc6359
• https://git.kernel.org/stable/c/abf3620cba68e0e51e5c21054ce4f925f75b3661
• https://git.kernel.org/stable/c/c8c80a3a35c2e3488409de2d5376ef7e662a2bf5
• https://git.kernel.org/stable/c/c529c3730bd09115684644e26bf01ecbd7e2c2c9