[PATCH 2/2] gpiolib: cdev: export the consumer's PID

Bartosz Golaszewski
2022-09-09T12:17:32Z

It's useful for user-space to be able to know the PIDs of processes
holding GPIO lines in case they have the permissions and need to kill
them.

Extend the gpio_v2_line_info structure with the consumer_pid field
that's set to the PID of the user-space process or 0 if the user lives
in the kernel.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
---
drivers/gpio/gpiolib-cdev.c | 2 ++
drivers/gpio/gpiolib.c | 24 +++++++++++++++++++-----
drivers/gpio/gpiolib.h | 2 ++
include/uapi/linux/gpio.h | 5 ++++-
4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f8041d4898d1..9b6d518680dc 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2120,6 +2120,8 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
if (desc->label)
strscpy(info->consumer, desc->label, sizeof(info->consumer));

+ info->consumer_pid = desc->pid;
+
/*
* Userspace only need to know that the kernel is using this GPIO so
* it can't use it.
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 6768734b9e15..0c9d1639b04d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -96,6 +96,11 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label)
d->label = label;
}

+static inline void desc_set_pid(struct gpio_desc *d, pid_t pid)
+{
+ d->pid = pid;
+}
+
/**
* gpio_to_desc - Convert a GPIO number to its descriptor
* @gpio: global GPIO number
@@ -1892,7 +1897,8 @@ EXPORT_SYMBOL_GPL(gpiochip_remove_pin_ranges);
* on each other, and help provide better diagnostics in debugfs.
* They're called even less than the "set direction" calls.
*/
-static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
+static int
+gpiod_request_commit(struct gpio_desc *desc, const char *label, pid_t pid)
{
struct gpio_chip *gc = desc->gdev->chip;
int ret;
@@ -1913,6 +1919,7 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)

if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
desc_set_label(desc, label ? : "?");
+ desc_set_pid(desc, pid);
} else {
ret = -EBUSY;
goto out_free_unlock;
@@ -1987,7 +1994,8 @@ static int validate_desc(const struct gpio_desc *desc, const char *func)
return; \
} while (0)

-int gpiod_request(struct gpio_desc *desc, const char *label)
+static int
+gpiod_request_with_pid(struct gpio_desc *desc, const char *label, pid_t pid)
{
int ret = -EPROBE_DEFER;
struct gpio_device *gdev;
@@ -1996,7 +2004,7 @@ int gpiod_request(struct gpio_desc *desc, const char *label)
gdev = desc->gdev;

if (try_module_get(gdev->owner)) {
- ret = gpiod_request_commit(desc, label);
+ ret = gpiod_request_commit(desc, label, pid);
if (ret)
module_put(gdev->owner);
else
@@ -2009,11 +2017,16 @@ int gpiod_request(struct gpio_desc *desc, const char *label)
return ret;
}

+int gpiod_request(struct gpio_desc *desc, const char *label)
+{
+ return gpiod_request_with_pid(desc, label, 0);
+}
+
int gpiod_request_user(struct gpio_desc *desc, const char *label)
{
int ret;

- ret = gpiod_request(desc, label);
+ ret = gpiod_request_with_pid(desc, label, current->pid);
if (ret == -EPROBE_DEFER)
ret = -ENODEV;

@@ -2042,6 +2055,7 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
}
kfree_const(desc->label);
desc_set_label(desc, NULL);
+ desc_set_pid(desc, 0);
clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
clear_bit(FLAG_REQUESTED, &desc->flags);
clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
@@ -2140,7 +2154,7 @@ struct gpio_desc *gpiochip_request_own_desc(struct gpio_chip *gc,
return desc;
}

- ret = gpiod_request_commit(desc, label);
+ ret = gpiod_request_commit(desc, label, 0);
if (ret < 0)
return ERR_PTR(ret);

diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index b35deb08a7f5..d1535677e162 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -165,6 +165,8 @@ struct gpio_desc {

/* Connection label */
const char *label;
+ /* Consumer's PID (if consumer is in user-space, otherwise 0) */
+ pid_t pid;
/* Name of the GPIO */
const char *name;
#ifdef CONFIG_OF_DYNAMIC
diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
index cb9966d49a16..37f10021d1aa 100644
--- a/include/uapi/linux/gpio.h
+++ b/include/uapi/linux/gpio.h
@@ -219,6 +219,8 @@ struct gpio_v2_line_request {
* gpio_v2_line_flag, such as %GPIO_V2_LINE_FLAG_ACTIVE_LOW,
* %GPIO_V2_LINE_FLAG_OUTPUT etc, added together.
* @attrs: the configuration attributes associated with the line
+ * @consumer_pid: process ID of the user-space consumer or 0 if the consumer
+ * lives in kernel space
* @padding: reserved for future use
*/
struct gpio_v2_line_info {
@@ -228,8 +230,9 @@ struct gpio_v2_line_info {
__u32 num_attrs;
__aligned_u64 flags;
struct gpio_v2_line_attribute attrs[GPIO_V2_LINE_NUM_ATTRS_MAX];
+ __s32 consumer_pid;
/* Space reserved for future use. */
- __u32 padding[4];
+ __u32 padding[3];
};

/**
--
2.34.1