CVE-2026-53194

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

USB: serial: kl5kusb105: fix bulk-out buffer overflow

klsi_105_prepare_write_buffer() is called by the generic write path

with the bulk-out buffer and its size (bulk_out_size, 64 bytes). It

stores a two-byte length header at the start of the buffer and copies

the payload from the write fifo starting at buf + KLSI_HDR_LEN, but

passes the full buffer size as the number of bytes to copy:

count = kfifo_out_locked(&port->write_fifo, buf + KLSI_HDR_LEN,

size, &port->lock);

When the fifo holds at least size bytes, size bytes are copied starting

two bytes into the size-byte buffer, writing KLSI_HDR_LEN bytes past its

end. Copy at most size - KLSI_HDR_LEN bytes instead, leaving room for

the header as safe_serial already does.

Writing bulk_out_size or more bytes to the tty triggers a slab

out-of-bounds write, observed with KASAN by emulating the device with

dummy_hcd and raw-gadget:

BUG: KASAN: slab-out-of-bounds in kfifo_copy_out+0x83/0xc0

Write of size 64 at addr ffff888112c62202 by task python3

kfifo_copy_out

klsi_105_prepare_write_buffer [kl5kusb105]

usb_serial_generic_write_start [usbserial]

Allocated by task 139:

usb_serial_probe [usbserial]

The buggy address is located 2 bytes inside of allocated 64-byte region

The out-of-bounds write no longer occurs with this change applied.