CVE-2024-50058

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

serial: protect uart_port_dtr_rts() in uart_shutdown() too

Commit af224ca2df29 (serial: core: Prevent unsafe uart port access, part
3) added few uport == NULL checks. It added one to uart_shutdown(), so
the commit assumes, uport can be NULL in there. But right after that
protection, there is an unprotected "uart_port_dtr_rts(uport, false);"
call. That is invoked only if HUPCL is set, so I assume that is the
reason why we do not see lots of these reports.

Or it cannot be NULL at this point at all for some reason :P.

Until the above is investigated, stay on the safe side and move this
dereference to the if too.

I got this inconsistency from Coverity under CID 1585130. Thanks.