From: Bartosz Golaszewski <brgl@bgdev.pl>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>
Subject: Re: [PATCH v1 1/2] gpiolib: Fix line event handling in compatible mode
Date: Tue, 10 Dec 2019 10:06:04 +0100 [thread overview]
Message-ID: <CAMRc=Mc88eiLtu7_0y51nGDzM0nRmwaOurLx9isf=qRB0uj7KA@mail.gmail.com> (raw)
In-Reply-To: <20191204194229.64251-1-andriy.shevchenko@linux.intel.com>
śr., 4 gru 2019 o 20:42 Andy Shevchenko
<andriy.shevchenko@linux.intel.com> napisał(a):
>
> The introduced line even handling ABI in the commit
>
> 61f922db7221 ("gpio: userspace ABI for reading GPIO line events")
>
> missed the fact that 64-bit kernel may serve for 32-bit applications.
> In such case the very first check in the lineevent_read() will fail
> due to alignment differences.
>
> To workaround this we do several things here:
> - put warning comment to UAPI header near to the structure description
> - derive the size of the structure in the compatible mode from its members
> - check for the size of this structure in the ->read() callback
> - return only one event in the compatible mode at a time
>
> Above mitigation will work at least with libgpiod which does one event
> at a time.
>
> Since the bug hasn't been reported earlier we assume that there is close
> to zero actual users of the compatible mode to monitor GPIO events and thus
> we might consider to rework this ABI in the future.
>
How come this only affects the read operation but not the structures
passed as arguments to ioctl() calls?
Bart
> Fixes: 61f922db7221 ("gpio: userspace ABI for reading GPIO line events")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> drivers/gpio/gpiolib.c | 51 ++++++++++++++++++++++++++++++++++++---
> include/uapi/linux/gpio.h | 6 +++++
> 2 files changed, 54 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 7340e4d0e873..134985210619 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -825,17 +825,26 @@ static __poll_t lineevent_poll(struct file *filep,
> return events;
> }
>
> -
> static ssize_t lineevent_read(struct file *filep,
> char __user *buf,
> size_t count,
> loff_t *f_ps)
> {
> struct lineevent_state *le = filep->private_data;
> + struct gpioevent_data event, *e = &event;
> + /* We need size of each member to avoid endianess issues below */
> + size_t ts_sz = sizeof(e->timestamp), id_sz = sizeof(e->id), e_sz;
> unsigned int copied;
> int ret;
>
> - if (count < sizeof(struct gpioevent_data))
> + /*
> + * In compatible mode, when kernel is 64-bit and user space is 32-bit,
> + * we may not tell what user wanted here when count is bigger than size
> + * of one event, so, we just assume that user asks for precisely one
> + * event.
> + */
> + e_sz = in_compat_syscall() ? ts_sz + id_sz : sizeof(*e);
> + if (count < e_sz)
> return -EINVAL;
>
> do {
> @@ -851,7 +860,43 @@ static ssize_t lineevent_read(struct file *filep,
>
> if (mutex_lock_interruptible(&le->read_lock))
> return -ERESTARTSYS;
> - ret = kfifo_to_user(&le->events, buf, count, &copied);
> + if (in_compat_syscall()) {
> + /*
> + * First we peek the one event and, if there is
> + * no error during copying to user space, skip it
> + * later.
> + */
> + if (kfifo_peek(&le->events, e))
> + copied = e_sz;
> + else
> + copied = 0;
> +
> + /* Do not try to copy garbage to the user */
> + ret = copied ? 0 : -EFAULT;
> +
> + /*
> + * Due to endianess concerns we have to copy this
> + * member-by-member. Luckily there are no members
> + * less than 32-bit.
> + */
> + if (!ret)
> + ret = copy_to_user(buf, &e->timestamp, ts_sz);
> + if (!ret)
> + ret = copy_to_user(buf + ts_sz, &e->id, id_sz);
> +
> + if (ret) {
> + /*
> + * Either we have got nothing from the FIFO or
> + * one of copy_to_user() calls failed.
> + */
> + ret = -EFAULT;
> + } else {
> + /* Skip peeked event if no error happened */
> + kfifo_skip(&le->events);
> + }
> + } else {
> + ret = kfifo_to_user(&le->events, buf, count, &copied);
> + }
> mutex_unlock(&le->read_lock);
>
> if (ret)
> diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> index 799cf823d493..054756bf6991 100644
> --- a/include/uapi/linux/gpio.h
> +++ b/include/uapi/linux/gpio.h
> @@ -168,6 +168,12 @@ struct gpioevent_request {
> * struct gpioevent_data - The actual event being pushed to userspace
> * @timestamp: best estimate of time of event occurrence, in nanoseconds
> * @id: event identifier
> + *
> + * Warning! This structure has issues in the compatible mode, when
> + * kernel is 64-bit and user space is 32-bit, due to alignment
> + * differences.
> + *
> + * It's not recommended to retrieve more than one event at a time.
> */
> struct gpioevent_data {
> __u64 timestamp;
> --
> 2.24.0
>
next prev parent reply other threads:[~2019-12-10 9:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-04 19:42 [PATCH v1 1/2] gpiolib: Fix line event handling in compatible mode Andy Shevchenko
2019-12-04 19:42 ` [PATCH v1 2/2] gpiolib: Make use of assign_bit() API Andy Shevchenko
2019-12-13 10:03 ` Linus Walleij
2019-12-06 10:57 ` [PATCH v1 1/2] gpiolib: Fix line event handling in compatible mode Bartosz Golaszewski
2019-12-10 9:06 ` Bartosz Golaszewski [this message]
2019-12-10 13:44 ` Andy Shevchenko
2019-12-10 14:39 ` Kent Gibson
2019-12-10 16:55 ` Andy Shevchenko
2019-12-11 9:18 ` Bartosz Golaszewski
2019-12-11 9:29 ` Kent Gibson
2019-12-11 10:47 ` Andy Shevchenko
2019-12-11 13:15 ` Bartosz Golaszewski
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