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: sc16is7xxstartup(): entry sc16is7xxmsproc(): entry sc16is7xxsettermios(): entry sc16is7xxsetbaud(): DLH/DLL = $009C --> access special register set sc16is7xxportirq() entry --> IIR is 0x0C sc16is7xxhandlerx() entry sc16is7xxfiforead(): --> unable to access FIFO (RHR) because it is mapped to DLL (LCR=LCRCONFMODEA) sc16is7xxsetbaud(): exit --> Restore access to general register set

Fix the problem by claiming the efr_lock mutex when accessing the Special register set.