CVE-2024-44950

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

serial: sc16is7xx: fix invalid FIFO access with special register set

When enabling access to the special register set, Receiver time-out and

RHR interrupts can happen. In this case, the IRQ handler will try to read

from the FIFO thru the RHR register at address 0x00, but address 0x00 is

mapped to DLL register, resulting in erroneous FIFO reading.

Call graph example:

sc16is7xx_startup(): entry

sc16is7xx_ms_proc(): entry

sc16is7xx_set_termios(): entry

sc16is7xx_set_baud(): DLH/DLL = $009C --> access special register set

sc16is7xx_port_irq() entry --> IIR is 0x0C

sc16is7xx_handle_rx() entry

sc16is7xx_fifo_read(): --> unable to access FIFO (RHR) because it is

mapped to DLL (LCR=LCR_CONF_MODE_A)

sc16is7xx_set_baud(): exit --> Restore access to general register set

Fix the problem by claiming the efr_lock mutex when accessing the Special

register set.