On 2022/6/20 15:53, Ilpo Järvinen wrote:
On Mon, 20 Jun 2022, Yi Yang wrote:
If port->mapbase = NULL in serial8250_request_std_resource() , it need
return a error code instead of 0. If uart_set_info() fail to request new
regions by serial8250_request_std_resource() but the return value of
serial8250_request_std_resource() is 0, that The system will mistakenly
considers that port resources are successfully applied for. A null
pointer reference is triggered when the port resource is later invoked.
The problem can also be triggered with the following simple program:
----------
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <errno.h>
struct serial_struct {
int type;
int line;
unsigned int port;
int irq;
int flags;
int xmit_fifo_size;
int custom_divisor;
int baud_base;
unsigned short close_delay;
char io_type;
char reserved_char[1];
int hub6;
unsigned short closing_wait; /* time to wait before closing */
unsigned short closing_wait2; /* no longer used... */
unsigned char *iomem_base;
unsigned short iomem_reg_shift;
unsigned int port_high;
unsigned long iomap_base; /* cookie passed into ioremap */
};
struct serial_struct str;
int main(void)
{
open("/dev/ttyS0", O_RDWR);
ioctl(fd, TIOCGSERIAL, &str);
str.iomem_base = 0;
ioctl(fd, TIOCSSERIAL, str);
return 0;
}
With admin priviledges I guess?
Yes, this program run on root.
----------
Signed-off-by: Yi Yang <yiyang13@xxxxxxxxxx>
---
drivers/tty/serial/8250/8250_port.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3e3d784aa628..e1cefa97bdeb 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2961,8 +2961,10 @@ static int serial8250_request_std_resource(struct uart_8250_port *up)
case UPIO_MEM32BE:
case UPIO_MEM16:
case UPIO_MEM:
- if (!port->mapbase)
+ if (!port->mapbase) {
+ ret = -EFAULT;
break;
+ }
if (!request_mem_region(port->mapbase, size, "serial")) {
ret = -EBUSY;
I recall reading somewhere that somebody more knowledgeful than me noted
that this interface has many ways to shoot oneself in the foot if one
really wants to which is why some things are limited to admin only.
I cannot seem to find that a reference to that now though.
Maybe some inadvertent behavior can be avoided.
The following code exists in uart_set_info():
If we fail to request resources for the new port, try to restore the old
settings. But uport->ops->release_port(uport) return value is 0.
----------
/*
* Free and release old regions
*/
if (old_type != PORT_UNKNOWN && uport->ops->release_port)
uport->ops->release_port(uport);
uport->iobase = new_port;
uport->type = new_info->type;
uport->hub6 = new_info->hub6;
uport->iotype = new_info->io_type;
uport->regshift = new_info->iomem_reg_shift;
uport->mapbase = (unsigned long)new_info->iomem_base;
/*
* Claim and map the new regions
*/
if (uport->type != PORT_UNKNOWN && uport->ops->request_port) {
retval = uport->ops->request_port(uport);
} else {
/* Always success - Jean II */
retval = 0;
}
/*
* If we fail to request resources for the
* new port, try to restore the old settings.
*/
if (retval) {
uport->iobase = old_iobase;
uport->type = old_type;
uport->hub6 = old_hub6;
uport->iotype = old_iotype;
uport->regshift = old_shift;
uport->mapbase = old_mapbase;
if (old_type != PORT_UNKNOWN) {
retval = uport->ops->request_port(uport);
/*
* If we failed to restore the old settings,
* we fail like this.
*/
if (retval)
uport->type = PORT_UNKNOWN;
/*
* We failed anyway.
*/
retval = -EBUSY;
}
----------
--
Yi
