Messages in this thread |  | | Subject | Re: [PATCH] kconfig: Add kernel config option for fuzz testing. | From | Tetsuo Handa <> | Date | Tue, 17 Dec 2019 21:54:02 +0900 |
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On 2019/12/17 17:41, Dmitry Vyukov wrote: >> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c >> index 90655910b0c7..367b92ad598b 100644 >> --- a/drivers/tty/serial/8250/8250_port.c >> +++ b/drivers/tty/serial/8250/8250_port.c >> @@ -519,11 +519,14 @@ serial_port_out_sync(struct uart_port *p, int offset, int value) >> case UPIO_MEM32: >> case UPIO_MEM32BE: >> case UPIO_AU: >> - p->serial_out(p, offset, value); >> + /* Writing to random kernel address causes crash. */ >> + if (!IS_ENABLED(CONFIG_KERNEL_BUILT_FOR_FUZZ_TESTING)) >> + p->serial_out(p, offset, value); > > Does this do the same as LOCKDOWN_TIOCSSERIAL? How is it different?
I don't know. If there were an oversight in condition of lines 852-858, uart_startup() might be called due to "goto check_and_exit;" without hitting security_locked_down(LOCKDOWN_TIOCSSERIAL) check.
846: old_flags = uport->flags; 847: new_flags = (__force upf_t)new_info->flags; 848: old_custom_divisor = uport->custom_divisor; 849: 850: if (!capable(CAP_SYS_ADMIN)) { 851: retval = -EPERM; 852: if (change_irq || change_port || 853: (new_info->baud_base != uport->uartclk / 16) || 854: (close_delay != port->close_delay) || 855: (closing_wait != port->closing_wait) || 856: (new_info->xmit_fifo_size && 857: new_info->xmit_fifo_size != uport->fifosize) || 858: (((new_flags ^ old_flags) & ~UPF_USR_MASK) != 0)) 859: goto exit; 860: uport->flags = ((uport->flags & ~UPF_USR_MASK) | 861: (new_flags & UPF_USR_MASK)); 862: uport->custom_divisor = new_info->custom_divisor; 863: goto check_and_exit; 864: } 865: 866: retval = security_locked_down(LOCKDOWN_TIOCSSERIAL); 867: if (retval && (change_irq || change_port)) 868: goto exit;
> >> p->serial_in(p, UART_LCR); /* safe, no side-effects */ >> break; >> default: >> - p->serial_out(p, offset, value); >> + if (!IS_ENABLED(CONFIG_KERNEL_BUILT_FOR_FUZZ_TESTING)) >> + p->serial_out(p, offset, value); >> } >> }
But I came think that "BUG: unable to handle kernel NULL pointer dereference in mem_serial_out" is a real kernel bug which should be fixed. It seems that crash occurs only when "struct serial_struct"->iomem_base == NULL, and EBUSY is returned otherwise. That is, some sanity check is wrong.
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