4a9a41650c
The problem is that ns8250_bus_probe() accesses a field from the ns8250_softc, which embeds the generic UART softc, but the ns8250_softc hasn't yet been allocated because we're still probing. This is a regression from commit 0aefb0a63c50. This fixed a problem where one of the upper four IER bits, which are usually reserved, needs to be set in order to get RX interrupts before the RX FIFO is full. At the same time, we avoid clearing those reserved bits (see commit 58957d87173, though other UART drivers I looked at do not bother with this). So, copy what ns8250_init() does to disable interrupts, since we don't know what the "right" mask is at this point. Reported by: syzbot+f256beefd0df9eb796e7@syzkaller.appspotmail.com Reviewed by: imp MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D31124
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