net: lan743x: fix potential out-of-bounds write in lan743x_ptp_io_event_clock_get()

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

net: lan743x: fix potential out-of-bounds write in lan743x_ptp_io_event_clock_get()

Before calling lan743x_ptp_io_event_clock_get(), the 'channel' value is checked against the maximum value of PCI11X1X_PTP_IO_MAX_CHANNELS(8). This seems correct and aligns with the PTP interrupt status register (PTP_INT_STS) specifications.

However, lan743x_ptp_io_event_clock_get() writes to ptp->extts[] with only LAN743X_PTP_N_EXTTS(4) elements, using channel as an index:

lan743x_ptp_io_event_clock_get(..., u8 channel,...) { ... /* Update Local timestamp */ extts = &ptp->extts[channel]; extts->ts.tv_sec = sec; ... }

To avoid an out-of-bounds write and utilize all the supported GPIO inputs, set LAN743X_PTP_N_EXTTS to 8.

Detected using the static analysis tool - Svace.