[PATCH 2/2] uio: Prevent device destruction while fds are open

From: Hamish Martin
Date: Thu May 10 2018 - 21:14:08 EST

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Prevent destruction of a uio_device while user space apps hold open
file descriptors to that device. Further, access to the 'info' member
of the struct uio_device is protected by spinlock. This is to ensure
stale pointers to data not under control of the UIO subsystem are not
dereferenced.

Signed-off-by: Hamish Martin <hamish.martin@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
---
drivers/uio/uio.c | 98 ++++++++++++++++++++++++++++++++++------------
include/linux/uio_driver.h | 3 +-
2 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index dd44df17004d..5473e77c85be 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -270,7 +270,7 @@ static int uio_dev_add_attributes(struct uio_device *idev)
if (!map_found) {
map_found = 1;
idev->map_dir = kobject_create_and_add("maps",
- &idev->dev->kobj);
+ &idev->dev.kobj);
if (!idev->map_dir) {
ret = -ENOMEM;
goto err_map;
@@ -299,7 +299,7 @@ static int uio_dev_add_attributes(struct uio_device *idev)
if (!portio_found) {
portio_found = 1;
idev->portio_dir = kobject_create_and_add("portio",
- &idev->dev->kobj);
+ &idev->dev.kobj);
if (!idev->portio_dir) {
ret = -ENOMEM;
goto err_portio;
@@ -342,7 +342,7 @@ static int uio_dev_add_attributes(struct uio_device *idev)
kobject_put(&map->kobj);
}
kobject_put(idev->map_dir);
- dev_err(idev->dev, "error creating sysfs files (%d)\n", ret);
+ dev_err(&idev->dev, "error creating sysfs files (%d)\n", ret);
return ret;
}

@@ -379,7 +379,7 @@ static int uio_get_minor(struct uio_device *idev)
idev->minor = retval;
retval = 0;
} else if (retval == -ENOSPC) {
- dev_err(idev->dev, "too many uio devices\n");
+ dev_err(&idev->dev, "too many uio devices\n");
retval = -EINVAL;
}
mutex_unlock(&minor_lock);
@@ -433,6 +433,7 @@ static int uio_open(struct inode *inode, struct file *filep)
struct uio_device *idev;
struct uio_listener *listener;
int ret = 0;
+ unsigned long flags;

mutex_lock(&minor_lock);
idev = idr_find(&uio_idr, iminor(inode));
@@ -442,9 +443,11 @@ static int uio_open(struct inode *inode, struct file *filep)
goto out;
}

+ get_device(&idev->dev);
+
if (!try_module_get(idev->owner)) {
ret = -ENODEV;
- goto out;
+ goto err_module_get;
}

listener = kmalloc(sizeof(*listener), GFP_KERNEL);
@@ -457,11 +460,13 @@ static int uio_open(struct inode *inode, struct file *filep)
listener->event_count = atomic_read(&idev->event);
filep->private_data = listener;

- if (idev->info->open) {
+ spin_lock_irqsave(&idev->info_lock, flags);
+ if (idev->info && idev->info->open)
ret = idev->info->open(idev->info, inode);
- if (ret)
- goto err_infoopen;
- }
+ spin_unlock_irqrestore(&idev->info_lock, flags);
+ if (ret)
+ goto err_infoopen;
+
return 0;

err_infoopen:
@@ -470,6 +475,9 @@ static int uio_open(struct inode *inode, struct file *filep)
err_alloc_listener:
module_put(idev->owner);

+err_module_get:
+ put_device(&idev->dev);
+
out:
return ret;
}
@@ -487,12 +495,16 @@ static int uio_release(struct inode *inode, struct file *filep)
int ret = 0;
struct uio_listener *listener = filep->private_data;
struct uio_device *idev = listener->dev;
+ unsigned long flags;

- if (idev->info->release)
+ spin_lock_irqsave(&idev->info_lock, flags);
+ if (idev->info && idev->info->release)
ret = idev->info->release(idev->info, inode);
+ spin_unlock_irqrestore(&idev->info_lock, flags);

module_put(idev->owner);
kfree(listener);
+ put_device(&idev->dev);
return ret;
}

@@ -500,9 +512,16 @@ static __poll_t uio_poll(struct file *filep, poll_table *wait)
{
struct uio_listener *listener = filep->private_data;
struct uio_device *idev = listener->dev;
+ __poll_t ret = 0;
+ unsigned long flags;

- if (!idev->info->irq)
- return -EIO;
+ spin_lock_irqsave(&idev->info_lock, flags);
+ if (!idev->info || !idev->info->irq)
+ ret = -EIO;
+ spin_unlock_irqrestore(&idev->info_lock, flags);
+
+ if (ret)
+ return ret;

poll_wait(filep, &idev->wait, wait);
if (listener->event_count != atomic_read(&idev->event))
@@ -516,11 +535,17 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
struct uio_listener *listener = filep->private_data;
struct uio_device *idev = listener->dev;
DECLARE_WAITQUEUE(wait, current);
- ssize_t retval;
+ ssize_t retval = 0;
s32 event_count;
+ unsigned long flags;

- if (!idev->info->irq)
- return -EIO;
+ spin_lock_irqsave(&idev->info_lock, flags);
+ if (!idev->info || !idev->info->irq)
+ retval = -EIO;
+ spin_unlock_irqrestore(&idev->info_lock, flags);
+
+ if (retval)
+ return retval;

if (count != sizeof(s32))
return -EINVAL;
@@ -567,8 +592,10 @@ static ssize_t uio_write(struct file *filep, const char __user *buf,
struct uio_device *idev = listener->dev;
ssize_t retval;
s32 irq_on;
+ unsigned long flags;

- if (!idev->info->irq) {
+ spin_lock_irqsave(&idev->info_lock, flags);
+ if (!idev->info || !idev->info->irq) {
retval = -EIO;
goto out;
}
@@ -591,6 +618,7 @@ static ssize_t uio_write(struct file *filep, const char __user *buf,
retval = idev->info->irqcontrol(idev->info, irq_on);

out:
+ spin_unlock_irqrestore(&idev->info_lock, flags);
return retval ? retval : sizeof(s32);
}

@@ -803,6 +831,13 @@ static void release_uio_class(void)
uio_major_cleanup();
}

+static void uio_device_release(struct device *dev)
+{
+ struct uio_device *idev = dev_get_drvdata(dev);
+
+ kfree(idev);
+}
+
/**
* uio_register_device - register a new userspace IO device
* @owner: module that creates the new device
@@ -823,13 +858,14 @@ int __uio_register_device(struct module *owner,

info->uio_dev = NULL;

- idev = devm_kzalloc(parent, sizeof(*idev), GFP_KERNEL);
+ idev = kzalloc(sizeof(*idev), GFP_KERNEL);
if (!idev) {
return -ENOMEM;
}

idev->owner = owner;
idev->info = info;
+ spin_lock_init(&idev->info_lock);
init_waitqueue_head(&idev->wait);
atomic_set(&idev->event, 0);

@@ -837,14 +873,19 @@ int __uio_register_device(struct module *owner,
if (ret)
return ret;

- idev->dev = device_create(&uio_class, parent,
- MKDEV(uio_major, idev->minor), idev,
- "uio%d", idev->minor);
- if (IS_ERR(idev->dev)) {
- printk(KERN_ERR "UIO: device register failed\n");
- ret = PTR_ERR(idev->dev);
+ idev->dev.devt = MKDEV(uio_major, idev->minor);
+ idev->dev.class = &uio_class;
+ idev->dev.parent = parent;
+ idev->dev.release = uio_device_release;
+ dev_set_drvdata(&idev->dev, idev);
+
+ ret = dev_set_name(&idev->dev, "uio%d", idev->minor);
+ if (ret)
+ goto err_device_create;
+
+ ret = device_register(&idev->dev);
+ if (ret)
goto err_device_create;
- }

ret = uio_dev_add_attributes(idev);
if (ret)
@@ -872,7 +913,7 @@ int __uio_register_device(struct module *owner,
err_request_irq:
uio_dev_del_attributes(idev);
err_uio_dev_add_attributes:
- device_destroy(&uio_class, MKDEV(uio_major, idev->minor));
+ device_unregister(&idev->dev);
err_device_create:
uio_free_minor(idev);
return ret;
@@ -887,6 +928,7 @@ EXPORT_SYMBOL_GPL(__uio_register_device);
void uio_unregister_device(struct uio_info *info)
{
struct uio_device *idev;
+ unsigned long flags;

if (!info || !info->uio_dev)
return;
@@ -900,7 +942,11 @@ void uio_unregister_device(struct uio_info *info)
if (info->irq && info->irq != UIO_IRQ_CUSTOM)
free_irq(info->irq, idev);

- device_destroy(&uio_class, MKDEV(uio_major, idev->minor));
+ spin_lock_irqsave(&idev->info_lock, flags);
+ idev->info = NULL;
+ spin_unlock_irqrestore(&idev->info_lock, flags);
+
+ device_unregister(&idev->dev);

return;
}
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 3c85c81b0027..42b3d7cd7413 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -68,12 +68,13 @@ struct uio_port {

struct uio_device {
struct module *owner;
- struct device *dev;
+ struct device dev;
int minor;
atomic_t event;
struct fasync_struct *async_queue;
wait_queue_head_t wait;
struct uio_info *info;
+ spinlock_t info_lock;
struct kobject *map_dir;
struct kobject *portio_dir;
};
--
2.16.2

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