CVE-2024-56670

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: u_serial: Fix the issue that gs_start_io crashed due to accessing null pointer

Considering that in some extreme cases, when u_serial driver is accessed by multiple threads, Thread A is executing the open operation and calling the gs_open, Thread B is executing the disconnect operation and calling the gserial_disconnect function,The port->port_usb pointer will be set to NULL.

E.g. Thread A Thread B gs_open() gadget_unbind_driver() gs_start_io() composite_disconnect() gs_start_rx() gserial_disconnect() … … spin_unlock(&port->port_lock) status = usb_ep_queue() spin_lock(&port->port_lock) spin_lock(&port->port_lock) port->port_usb = NULL gs_free_requests(port->port_usb->in) spin_unlock(&port->port_lock) Crash

This causes thread A to access a null pointer (port->port_usb is null) when calling the gs_free_requests function, causing a crash.

If port_usb is NULL, the release request will be skipped as it will be done by gserial_disconnect.

So add a null pointer check to gs_start_io before attempting to access the value of the pointer port->port_usb.

Call trace: gs_start_io+0x164/0x25c gs_open+0x108/0x13c tty_open+0x314/0x638 chrdev_open+0x1b8/0x258 do_dentry_open+0x2c4/0x700 vfs_open+0x2c/0x3c path_openat+0xa64/0xc60 do_filp_open+0xb8/0x164 do_sys_openat2+0x84/0xf0 __arm64_sys_openat+0x70/0x9c invoke_syscall+0x58/0x114 el0_svc_common+0x80/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x38/0x68

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/1247e1df086aa6c17ab53cd1bedce70dd7132765
• https://git.kernel.org/stable/c/28b3c03a6790de1f6f2683919ad657840f0f0f58
• https://git.kernel.org/stable/c/4cfbca86f6a8b801f3254e0e3c8f2b1d2d64be2b
• https://git.kernel.org/stable/c/4efdfdc32d8d6307f968cd99f1db64468471bab1
• https://git.kernel.org/stable/c/8ca07a3d18f39b1669927ef536e485787e856df6
• https://git.kernel.org/stable/c/c83213b6649d22656b3a4e92544ceeea8a2c6c07
• https://git.kernel.org/stable/c/dd6b0ca6025f64ccb465a6a3460c5b0307ed9c44