[3/5] hwrng: core - Do not register device opportunistically
diff mbox series

Message ID E1Y3ICh-0007d7-SM@gondolin.me.apana.org.au
State New, archived
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Series
  • hwrng: Fix kref warning and underlying bugs
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Commit Message

Herbert Xu Dec. 23, 2014, 5:40 a.m. UTC
Currently we only register the device when a valid RNG is added.
However the way it's done is buggy because we test whether there
is a current RNG to determine whether we need to register.  As
the current RNG may be missing due to a reinitialisation error
this can lead to a reregistration of the device.

As the device already has to handle a NULL current RNG anyway,
let's just register the device always and remove the complexity.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---

 drivers/char/hw_random/core.c |   23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

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Comments

Rusty Russell Dec. 23, 2014, 11:29 p.m. UTC | #1
Herbert Xu <herbert@gondor.apana.org.au> writes:
> Currently we only register the device when a valid RNG is added.
> However the way it's done is buggy because we test whether there
> is a current RNG to determine whether we need to register.  As
> the current RNG may be missing due to a reinitialisation error
> this can lead to a reregistration of the device.
>
> As the device already has to handle a NULL current RNG anyway,
> let's just register the device always and remove the complexity.

Does this break userspace by creating a device which will just return
-ENODEV on read?  Sure, callers *should* handle it...

I far prefer this (simpler) model, though.

Thanks,
Rusty.

>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> ---
>
>  drivers/char/hw_random/core.c |   23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 42827fd..1d342f0 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -372,14 +372,14 @@ static DEVICE_ATTR(rng_available, S_IRUGO,
>  		   NULL);
>  
>  
> -static void unregister_miscdev(void)
> +static void __exit unregister_miscdev(void)
>  {
>  	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
>  	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
>  	misc_deregister(&rng_miscdev);
>  }
>  
> -static int register_miscdev(void)
> +static int __init register_miscdev(void)
>  {
>  	int err;
>  
> @@ -484,12 +484,6 @@ int hwrng_register(struct hwrng *rng)
>  		if (err)
>  			goto out_unlock;
>  		set_current_rng(rng);
> -
> -		err = register_miscdev();
> -		if (err) {
> -			drop_current_rng();
> -			goto out_unlock;
> -		}
>  	}
>  	list_add_tail(&rng->list, &rng_list);
>  
> @@ -530,7 +524,6 @@ void hwrng_unregister(struct hwrng *rng)
>  
>  	if (list_empty(&rng_list)) {
>  		mutex_unlock(&rng_mutex);
> -		unregister_miscdev();
>  		if (hwrng_fill)
>  			kthread_stop(hwrng_fill);
>  	} else
> @@ -540,16 +533,24 @@ void hwrng_unregister(struct hwrng *rng)
>  }
>  EXPORT_SYMBOL_GPL(hwrng_unregister);
>  
> -static void __exit hwrng_exit(void)
> +static int __init hwrng_modinit(void)
> +{
> +	return register_miscdev();
> +}
> +
> +static void __exit hwrng_modexit(void)
>  {
>  	mutex_lock(&rng_mutex);
>  	BUG_ON(current_rng);
>  	kfree(rng_buffer);
>  	kfree(rng_fillbuf);
>  	mutex_unlock(&rng_mutex);
> +
> +	unregister_miscdev();
>  }
>  
> -module_exit(hwrng_exit);
> +module_init(hwrng_modinit);
> +module_exit(hwrng_modexit);
>  
>  MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
>  MODULE_LICENSE("GPL");
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Herbert Xu Dec. 26, 2014, 1 a.m. UTC | #2
On Wed, Dec 24, 2014 at 09:59:41AM +1030, Rusty Russell wrote:
>
> Does this break userspace by creating a device which will just return
> -ENODEV on read?  Sure, callers *should* handle it...

If somebody complains we could easily fix this by making open
fail.  In fact, if such applications exist then they're likely
to want to hold onto a reference to the RNG after then open...

Cheers,

Patch
diff mbox series

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 42827fd..1d342f0 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -372,14 +372,14 @@  static DEVICE_ATTR(rng_available, S_IRUGO,
 		   NULL);
 
 
-static void unregister_miscdev(void)
+static void __exit unregister_miscdev(void)
 {
 	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 	device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 	misc_deregister(&rng_miscdev);
 }
 
-static int register_miscdev(void)
+static int __init register_miscdev(void)
 {
 	int err;
 
@@ -484,12 +484,6 @@  int hwrng_register(struct hwrng *rng)
 		if (err)
 			goto out_unlock;
 		set_current_rng(rng);
-
-		err = register_miscdev();
-		if (err) {
-			drop_current_rng();
-			goto out_unlock;
-		}
 	}
 	list_add_tail(&rng->list, &rng_list);
 
@@ -530,7 +524,6 @@  void hwrng_unregister(struct hwrng *rng)
 
 	if (list_empty(&rng_list)) {
 		mutex_unlock(&rng_mutex);
-		unregister_miscdev();
 		if (hwrng_fill)
 			kthread_stop(hwrng_fill);
 	} else
@@ -540,16 +533,24 @@  void hwrng_unregister(struct hwrng *rng)
 }
 EXPORT_SYMBOL_GPL(hwrng_unregister);
 
-static void __exit hwrng_exit(void)
+static int __init hwrng_modinit(void)
+{
+	return register_miscdev();
+}
+
+static void __exit hwrng_modexit(void)
 {
 	mutex_lock(&rng_mutex);
 	BUG_ON(current_rng);
 	kfree(rng_buffer);
 	kfree(rng_fillbuf);
 	mutex_unlock(&rng_mutex);
+
+	unregister_miscdev();
 }
 
-module_exit(hwrng_exit);
+module_init(hwrng_modinit);
+module_exit(hwrng_modexit);
 
 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 MODULE_LICENSE("GPL");