gpiolib: protect the GPIO device against being dropped while in use by user-space

While any of the GPIO cdev syscalls is in progress, the kernel can call
gpiochip_remove() (for instance, when a USB GPIO expander is disconnected)
which will set gdev->chip to NULL after which any subsequent access will
cause a crash.

To avoid that: use an RW-semaphore in which the syscalls take it for
reading (so that we don't needlessly prohibit the user-space from calling
syscalls simultaneously) while gpiochip_remove() takes it for writing so
that it can only happen once all syscalls return.

Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines")
Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL")
Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
Fixes: a54756cb24ea ("gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL")
Fixes: 7b8e00d98168 ("gpiolib: cdev: support GPIO_V2_LINE_SET_VALUES_IOCTL")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
[Nick: fixed a build failure with CDEV_V1 disabled]
Co-authored-by: Nick Hainke <vincent@systemli.org>
Reviewed-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index ac10c9494bf02882faeef05e251e0fb5cbe8e5a0..f7289c2f3a3c3d238c56dc4c516dc4289e680555 100644 (file)
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -55,6 +55,50 @@ static_assert(IS_ALIGNED(sizeof(struct gpio_v2_line_values), 8));
  * interface to gpiolib GPIOs via ioctl()s.
  */
 
+typedef __poll_t (*poll_fn)(struct file *, struct poll_table_struct *);
+typedef long (*ioctl_fn)(struct file *, unsigned int, unsigned long);
+typedef ssize_t (*read_fn)(struct file *, char __user *,
+                          size_t count, loff_t *);
+
+static __poll_t call_poll_locked(struct file *file,
+                                struct poll_table_struct *wait,
+                                struct gpio_device *gdev, poll_fn func)
+{
+       __poll_t ret;
+
+       down_read(&gdev->sem);
+       ret = func(file, wait);
+       up_read(&gdev->sem);
+
+       return ret;
+}
+
+static long call_ioctl_locked(struct file *file, unsigned int cmd,
+                             unsigned long arg, struct gpio_device *gdev,
+                             ioctl_fn func)
+{
+       long ret;
+
+       down_read(&gdev->sem);
+       ret = func(file, cmd, arg);
+       up_read(&gdev->sem);
+
+       return ret;
+}
+
+static ssize_t call_read_locked(struct file *file, char __user *buf,
+                               size_t count, loff_t *f_ps,
+                               struct gpio_device *gdev, read_fn func)
+{
+       ssize_t ret;
+
+       down_read(&gdev->sem);
+       ret = func(file, buf, count, f_ps);
+       up_read(&gdev->sem);
+
+       return ret;
+}
+
 /*
  * GPIO line handle management
  */
@@ -191,8 +235,8 @@ static long linehandle_set_config(struct linehandle_state *lh,
        return 0;
 }
 
-static long linehandle_ioctl(struct file *file, unsigned int cmd,
-                            unsigned long arg)
+static long linehandle_ioctl_unlocked(struct file *file, unsigned int cmd,
+                                     unsigned long arg)
 {
        struct linehandle_state *lh = file->private_data;
        void __user *ip = (void __user *)arg;
@@ -250,6 +294,15 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
        }
 }
 
+static long linehandle_ioctl(struct file *file, unsigned int cmd,
+                            unsigned long arg)
+{
+       struct linehandle_state *lh = file->private_data;
+
+       return call_ioctl_locked(file, cmd, arg, lh->gdev,
+                                linehandle_ioctl_unlocked);
+}
+
 #ifdef CONFIG_COMPAT
 static long linehandle_ioctl_compat(struct file *file, unsigned int cmd,
                                    unsigned long arg)
@@ -1381,8 +1434,8 @@ static long linereq_set_config(struct linereq *lr, void __user *ip)
        return ret;
 }
 
-static long linereq_ioctl(struct file *file, unsigned int cmd,
-                         unsigned long arg)
+static long linereq_ioctl_unlocked(struct file *file, unsigned int cmd,
+                                  unsigned long arg)
 {
        struct linereq *lr = file->private_data;
        void __user *ip = (void __user *)arg;
@@ -1402,6 +1455,15 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
        }
 }
 
+static long linereq_ioctl(struct file *file, unsigned int cmd,
+                         unsigned long arg)
+{
+       struct linereq *lr = file->private_data;
+
+       return call_ioctl_locked(file, cmd, arg, lr->gdev,
+                                linereq_ioctl_unlocked);
+}
+
 #ifdef CONFIG_COMPAT
 static long linereq_ioctl_compat(struct file *file, unsigned int cmd,
                                 unsigned long arg)
@@ -1410,8 +1472,8 @@ static long linereq_ioctl_compat(struct file *file, unsigned int cmd,
 }
 #endif
 
-static __poll_t linereq_poll(struct file *file,
-                           struct poll_table_struct *wait)
+static __poll_t linereq_poll_unlocked(struct file *file,
+                                     struct poll_table_struct *wait)
 {
        struct linereq *lr = file->private_data;
        __poll_t events = 0;
@@ -1428,10 +1490,16 @@ static __poll_t linereq_poll(struct file *file,
        return events;
 }
 
-static ssize_t linereq_read(struct file *file,
-                           char __user *buf,
-                           size_t count,
-                           loff_t *f_ps)
+static __poll_t linereq_poll(struct file *file,
+                            struct poll_table_struct *wait)
+{
+       struct linereq *lr = file->private_data;
+
+       return call_poll_locked(file, wait, lr->gdev, linereq_poll_unlocked);
+}
+
+static ssize_t linereq_read_unlocked(struct file *file, char __user *buf,
+                                    size_t count, loff_t *f_ps)
 {
        struct linereq *lr = file->private_data;
        struct gpio_v2_line_event le;
@@ -1485,6 +1553,15 @@ static ssize_t linereq_read(struct file *file,
        return bytes_read;
 }
 
+static ssize_t linereq_read(struct file *file, char __user *buf,
+                           size_t count, loff_t *f_ps)
+{
+       struct linereq *lr = file->private_data;
+
+       return call_read_locked(file, buf, count, f_ps, lr->gdev,
+                               linereq_read_unlocked);
+}
+
 static void linereq_free(struct linereq *lr)
 {
        unsigned int i;
@@ -1722,8 +1799,8 @@ struct lineevent_state {
        (GPIOEVENT_REQUEST_RISING_EDGE | \
        GPIOEVENT_REQUEST_FALLING_EDGE)
 
-static __poll_t lineevent_poll(struct file *file,
-                              struct poll_table_struct *wait)
+static __poll_t lineevent_poll_unlocked(struct file *file,
+                                       struct poll_table_struct *wait)
 {
        struct lineevent_state *le = file->private_data;
        __poll_t events = 0;
@@ -1739,15 +1816,21 @@ static __poll_t lineevent_poll(struct file *file,
        return events;
 }
 
+static __poll_t lineevent_poll(struct file *file,
+                              struct poll_table_struct *wait)
+{
+       struct lineevent_state *le = file->private_data;
+
+       return call_poll_locked(file, wait, le->gdev, lineevent_poll_unlocked);
+}
+
 struct compat_gpioeevent_data {
        compat_u64      timestamp;
        u32             id;
 };
 
-static ssize_t lineevent_read(struct file *file,
-                             char __user *buf,
-                             size_t count,
-                             loff_t *f_ps)
+static ssize_t lineevent_read_unlocked(struct file *file, char __user *buf,
+                                      size_t count, loff_t *f_ps)
 {
        struct lineevent_state *le = file->private_data;
        struct gpioevent_data ge;
@@ -1815,6 +1898,15 @@ static ssize_t lineevent_read(struct file *file,
        return bytes_read;
 }
 
+static ssize_t lineevent_read(struct file *file, char __user *buf,
+                             size_t count, loff_t *f_ps)
+{
+       struct lineevent_state *le = file->private_data;
+
+       return call_read_locked(file, buf, count, f_ps, le->gdev,
+                               lineevent_read_unlocked);
+}
+
 static void lineevent_free(struct lineevent_state *le)
 {
        if (le->irq)
@@ -1832,8 +1924,8 @@ static int lineevent_release(struct inode *inode, struct file *file)
        return 0;
 }
 
-static long lineevent_ioctl(struct file *file, unsigned int cmd,
-                           unsigned long arg)
+static long lineevent_ioctl_unlocked(struct file *file, unsigned int cmd,
+                                    unsigned long arg)
 {
        struct lineevent_state *le = file->private_data;
        void __user *ip = (void __user *)arg;
@@ -1864,6 +1956,15 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
        return -EINVAL;
 }
 
+static long lineevent_ioctl(struct file *file, unsigned int cmd,
+                           unsigned long arg)
+{
+       struct lineevent_state *le = file->private_data;
+
+       return call_ioctl_locked(file, cmd, arg, le->gdev,
+                                lineevent_ioctl_unlocked);
+}
+
 #ifdef CONFIG_COMPAT
 static long lineevent_ioctl_compat(struct file *file, unsigned int cmd,
                                   unsigned long arg)
@@ -2422,8 +2523,8 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
        return NOTIFY_OK;
 }
 
-static __poll_t lineinfo_watch_poll(struct file *file,
-                                   struct poll_table_struct *pollt)
+static __poll_t lineinfo_watch_poll_unlocked(struct file *file,
+                                            struct poll_table_struct *pollt)
 {
        struct gpio_chardev_data *cdev = file->private_data;
        __poll_t events = 0;
@@ -2440,8 +2541,17 @@ static __poll_t lineinfo_watch_poll(struct file *file,
        return events;
 }
 
-static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
-                                  size_t count, loff_t *off)
+static __poll_t lineinfo_watch_poll(struct file *file,
+                                   struct poll_table_struct *pollt)
+{
+       struct gpio_chardev_data *cdev = file->private_data;
+
+       return call_poll_locked(file, pollt, cdev->gdev,
+                               lineinfo_watch_poll_unlocked);
+}
+
+static ssize_t lineinfo_watch_read_unlocked(struct file *file, char __user *buf,
+                                           size_t count, loff_t *off)
 {
        struct gpio_chardev_data *cdev = file->private_data;
        struct gpio_v2_line_info_changed event;
@@ -2519,6 +2629,15 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
        return bytes_read;
 }
 
+static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
+                                  size_t count, loff_t *off)
+{
+       struct gpio_chardev_data *cdev = file->private_data;
+
+       return call_read_locked(file, buf, count, off, cdev->gdev,
+                               lineinfo_watch_read_unlocked);
+}
+
 /**
  * gpio_chrdev_open() - open the chardev for ioctl operations
  * @inode: inode for this chardev
@@ -2532,13 +2651,17 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
        struct gpio_chardev_data *cdev;
        int ret = -ENOMEM;
 
+       down_read(&gdev->sem);
+
        /* Fail on open if the backing gpiochip is gone */
-       if (!gdev->chip)
-               return -ENODEV;
+       if (!gdev->chip) {
+               ret = -ENODEV;
+               goto out_unlock;
+       }
 
        cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
        if (!cdev)
-               return -ENOMEM;
+               goto out_unlock;
 
        cdev->watched_lines = bitmap_zalloc(gdev->chip->ngpio, GFP_KERNEL);
        if (!cdev->watched_lines)
@@ -2561,6 +2684,8 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
        if (ret)
                goto out_unregister_notifier;
 
+       up_read(&gdev->sem);
+
        return ret;
 
 out_unregister_notifier:
@@ -2570,6 +2695,8 @@ out_free_bitmap:
        bitmap_free(cdev->watched_lines);
 out_free_cdev:
        kfree(cdev);
+out_unlock:
+       up_read(&gdev->sem);
        return ret;
 }
 

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 0058ee83989df17496ccccb803b19542a36602eb..b8e17a4e38c519b5bfaab987271d4d3be2796686 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -790,6 +790,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
        spin_unlock_irqrestore(&gpio_lock, flags);
 
        BLOCKING_INIT_NOTIFIER_HEAD(&gdev->notifier);
+       init_rwsem(&gdev->sem);
 
 #ifdef CONFIG_PINCTRL
        INIT_LIST_HEAD(&gdev->pin_ranges);
@@ -924,6 +925,8 @@ void gpiochip_remove(struct gpio_chip *gc)
        unsigned long   flags;
        unsigned int    i;
 
+       down_write(&gdev->sem);
+
        /* FIXME: should the legacy sysfs handling be moved to gpio_device? */
        gpiochip_sysfs_unregister(gdev);
        gpiochip_free_hogs(gc);
@@ -958,6 +961,7 @@ void gpiochip_remove(struct gpio_chip *gc)
         * gone.
         */
        gcdev_unregister(gdev);
+       up_write(&gdev->sem);
        put_device(&gdev->dev);
 }
 EXPORT_SYMBOL_GPL(gpiochip_remove);

diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index e443c1023a3744a9f03776c07caf4323f8633fd3..b3c2db6eba80cbb05f1490b476b0e7f761fa070a 100644 (file)
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -15,6 +15,7 @@
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/cdev.h>
+#include <linux/rwsem.h>
 
 #define GPIOCHIP_NAME  "gpiochip"
 
@@ -39,6 +40,9 @@
  * @list: links gpio_device:s together for traversal
  * @notifier: used to notify subscribers about lines being requested, released
  *            or reconfigured
+ * @sem: protects the structure from a NULL-pointer dereference of @chip by
+ *       user-space operations when the device gets unregistered during
+ *       a hot-unplug event
  * @pin_ranges: range of pins served by the GPIO driver
  *
  * This state container holds most of the runtime variable data
@@ -60,6 +64,7 @@ struct gpio_device {
        void                    *data;
        struct list_head        list;
        struct blocking_notifier_head notifier;
+       struct rw_semaphore     sem;
 
 #ifdef CONFIG_PINCTRL
        /*