[PATCH 0/2] gpiolib: linehandle_ioctl() tweaks

[PATCH 0/2] gpiolib: linehandle_ioctl() tweaks

[Bartosz Golaszewski]

I noticed that - unlike sysfs - it's possible to set values of input
lines from user space using the character device. There's actually
even a TODO in the linehandle_ioctl() code.

This is not correct so the first patches fixes that and the second
removes a TODO that's not really needed.

Bartosz Golaszewski (2):
  gpiolib: don't allow userspace to set values of input lines
  gpiolib: remove an unneccessary TODO

 drivers/gpio/gpiolib.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

-- 
2.17.1

[PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

[Bartosz Golaszewski]

User space can currently both read and set values of input lines using
the character device. This was not allowed by the old sysfs interface
nor is it a correct behavior.

Check the first descriptor in the set for the OUT flag when asked to
set values and return -EPERM if the line is input.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
---
 drivers/gpio/gpiolib.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e11a3bb03820..57973524360d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -449,7 +449,13 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
 
 		return 0;
 	} else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
-		/* TODO: check if descriptors are really output */
+		/*
+		 * All line descriptors were created at once with the same
+		 * flags so just check if the first one is really output.
+		 */
+		if (!test_bit(FLAG_IS_OUT, &lh->descs[0]->flags))
+			return -EPERM;
+
 		if (copy_from_user(&ghd, ip, sizeof(ghd)))
 			return -EFAULT;
 
-- 
2.17.1

Re: [PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

[Linus Walleij]

On Mon, Jul 16, 2018 at 10:34 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> User space can currently both read and set values of input lines using
> the character device. This was not allowed by the old sysfs interface
> nor is it a correct behavior.
>
> Check the first descriptor in the set for the OUT flag when asked to
> set values and return -EPERM if the line is input.
>
> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Patch applied! Thanks for fixing this.

>         } else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
> -               /* TODO: check if descriptors are really output */

I wonder what kind of lazy coder leaves this kind of garbage
behind for others to fix up...

d7c51b47ac11e (Linus Walleij           2016-04-26 10:35:29 +0200  451)
 } else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
d7c51b47ac11e (Linus Walleij           2016-04-26 10:35:29 +0200  452)
         /* TODO: check if descriptors are really output */
d7c51b47ac11e (Linus Walleij           2016-04-26 10:35:29 +0200  453)
         if (copy_from_user(&ghd, ip, sizeof(ghd)))

Oh that guy.

Yours,
Linus Walleij

Re: [PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

[Bartosz Golaszewski]

2018-07-16 15:40 GMT+02:00 Linus Walleij <linus.walleij@linaro.org>:
> On Mon, Jul 16, 2018 at 10:34 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
>> User space can currently both read and set values of input lines using
>> the character device. This was not allowed by the old sysfs interface
>> nor is it a correct behavior.
>>
>> Check the first descriptor in the set for the OUT flag when asked to
>> set values and return -EPERM if the line is input.
>>
>> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
>
> Patch applied! Thanks for fixing this.
>

Thanks. Do you think we should Cc stable on that one?

Bart

Re: [PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

[Linus Walleij]

On Mon, Jul 16, 2018 at 4:13 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> 2018-07-16 15:40 GMT+02:00 Linus Walleij <linus.walleij@linaro.org>:
> > On Mon, Jul 16, 2018 at 10:34 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >
> >> User space can currently both read and set values of input lines using
> >> the character device. This was not allowed by the old sysfs interface
> >> nor is it a correct behavior.
> >>
> >> Check the first descriptor in the set for the OUT flag when asked to
> >> set values and return -EPERM if the line is input.
> >>
> >> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
> >
> > Patch applied! Thanks for fixing this.
>
> Thanks. Do you think we should Cc stable on that one?

Nah. It's not a regression. (Not like things that worked before
stopped working.)

Yours,
Linus Walleij

[PATCH 2/2] gpiolib: remove an unnecessary TODO

[Bartosz Golaszewski]

It's actually fine to read values of output lines. This was also
allowed by the legacy sysfs interface.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
---
 drivers/gpio/gpiolib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 57973524360d..19d36698574b 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -431,7 +431,7 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
 	int i;
 
 	if (cmd == GPIOHANDLE_GET_LINE_VALUES_IOCTL) {
-		/* TODO: check if descriptors are really input */
+		/* NOTE: It's ok to read values of output lines. */
 		int ret = gpiod_get_array_value_complex(false,
 							true,
 							lh->numdescs,
-- 
2.17.1

Re: [PATCH 2/2] gpiolib: remove an unnecessary TODO

[Linus Walleij]

On Mon, Jul 16, 2018 at 10:34 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> It's actually fine to read values of output lines. This was also
> allowed by the legacy sysfs interface.
>
> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Patch applied.

Yours,
Linus Walleij