[PATCH v2] staging: pi433: fix race condition in pi433_ioctl

[PATCH v2] staging: pi433: fix race condition in pi433_ioctl

[Hugo Lefeuvre]

In the PI433_IOC_WR_TX_CFG case in pi433_ioctl, instance->tx_cfg is
modified via

copy_from_user(&instance->tx_cfg, argp, sizeof(struct pi433_tx_cfg)))

without any kind of synchronization. In the case where two threads
would execute this same command concurrently the tx_cfg field might
enter in an inconsistent state.

Additionally: if ioctl(PI433_IOC_WR_TX_CFG) and write() execute
concurrently the tx config might be modified while it is being
copied to the fifo, resulting in potential data corruption.

Fix: Get instance->tx_cfg_lock before modifying tx config in the
PI433_IOC_WR_TX_CFG case in pi433_ioctl.

Also, do not copy data directly from user space to instance->tx_cfg.
Instead use a temporary buffer allowing future checks for correctness
of copied data.

Signed-off-by: Hugo Lefeuvre <hle@owl.eu.com>
---
Changes in v2:
    - Use device->tx_fifo_lock instead of introducing a new lock in
      instance.
    - Do not copy data directly from user space to instance->tx_cfg,
      instead use a temporary buffer allowing future checks for
      correctness of copied data.
---
 drivers/staging/pi433/pi433_if.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
index b061f77dda41..3ec1ed01d04b 100644
--- a/drivers/staging/pi433/pi433_if.c
+++ b/drivers/staging/pi433/pi433_if.c
@@ -880,6 +880,7 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	int			retval = 0;
 	struct pi433_instance	*instance;
 	struct pi433_device	*device;
+	struct pi433_tx_cfg	tx_cfg_buffer;
 	void __user *argp = (void __user *)arg;
 
 	/* Check type and command number */
@@ -902,9 +903,15 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			return -EFAULT;
 		break;
 	case PI433_IOC_WR_TX_CFG:
-		if (copy_from_user(&instance->tx_cfg, argp,
-				   sizeof(struct pi433_tx_cfg)))
+		/* do not modify tx config while it is being copied to fifo */
+		mutex_lock(&device->tx_fifo_lock);
+		if (copy_from_user(&tx_cfg_buffer, argp,
+				   sizeof(struct pi433_tx_cfg))) {
+			mutex_unlock(&device->tx_fifo_lock);
 			return -EFAULT;
+		}
+		memcpy(&instance->tx_cfg, &tx_cfg_buffer, sizeof(struct pi433_tx_cfg));
+		mutex_unlock(&device->tx_fifo_lock);
 		break;
 	case PI433_IOC_RD_RX_CFG:
 		if (copy_to_user(argp, &device->rx_cfg,
-- 
2.17.1

Re: [PATCH v2] staging: pi433: fix race condition in pi433_ioctl

[Dan Carpenter]

On Tue, Jun 12, 2018 at 09:47:41PM -0400, Hugo Lefeuvre wrote:
> In the PI433_IOC_WR_TX_CFG case in pi433_ioctl, instance->tx_cfg is
> modified via
> 
> copy_from_user(&instance->tx_cfg, argp, sizeof(struct pi433_tx_cfg)))
> 
> without any kind of synchronization. In the case where two threads
> would execute this same command concurrently the tx_cfg field might
> enter in an inconsistent state.
> 
> Additionally: if ioctl(PI433_IOC_WR_TX_CFG) and write() execute
> concurrently the tx config might be modified while it is being
> copied to the fifo, resulting in potential data corruption.
> 
> Fix: Get instance->tx_cfg_lock before modifying tx config in the
> PI433_IOC_WR_TX_CFG case in pi433_ioctl.
> 
> Also, do not copy data directly from user space to instance->tx_cfg.
> Instead use a temporary buffer allowing future checks for correctness
> of copied data.
> 
> Signed-off-by: Hugo Lefeuvre <hle@owl.eu.com>
> ---
> Changes in v2:
>     - Use device->tx_fifo_lock instead of introducing a new lock in
>       instance.
>     - Do not copy data directly from user space to instance->tx_cfg,
>       instead use a temporary buffer allowing future checks for
>       correctness of copied data.
> ---
>  drivers/staging/pi433/pi433_if.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
> index b061f77dda41..3ec1ed01d04b 100644
> --- a/drivers/staging/pi433/pi433_if.c
> +++ b/drivers/staging/pi433/pi433_if.c
> @@ -880,6 +880,7 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  	int			retval = 0;
>  	struct pi433_instance	*instance;
>  	struct pi433_device	*device;
> +	struct pi433_tx_cfg	tx_cfg_buffer;
>  	void __user *argp = (void __user *)arg;
>  
>  	/* Check type and command number */
> @@ -902,9 +903,15 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  			return -EFAULT;
>  		break;
>  	case PI433_IOC_WR_TX_CFG:
> -		if (copy_from_user(&instance->tx_cfg, argp,
> -				   sizeof(struct pi433_tx_cfg)))
> +		/* do not modify tx config while it is being copied to fifo */
> +		mutex_lock(&device->tx_fifo_lock);
> +		if (copy_from_user(&tx_cfg_buffer, argp,
> +				   sizeof(struct pi433_tx_cfg))) {
> +			mutex_unlock(&device->tx_fifo_lock);
>  			return -EFAULT;
> +		}
> +		memcpy(&instance->tx_cfg, &tx_cfg_buffer, sizeof(struct pi433_tx_cfg));
> +		mutex_unlock(&device->tx_fifo_lock);

The lock is only needed around the memcpy() and that makes the code a
bit simpler as well.

regards,
dan carpenter

Re: [PATCH v2] staging: pi433: fix race condition in pi433_ioctl

[Dan Carpenter]

On Tue, Jun 12, 2018 at 09:47:41PM -0400, Hugo Lefeuvre wrote:
>  drivers/staging/pi433/pi433_if.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
> index b061f77dda41..3ec1ed01d04b 100644
> --- a/drivers/staging/pi433/pi433_if.c
> +++ b/drivers/staging/pi433/pi433_if.c
> @@ -880,6 +880,7 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  	int			retval = 0;
>  	struct pi433_instance	*instance;
>  	struct pi433_device	*device;
> +	struct pi433_tx_cfg	tx_cfg_buffer;
>  	void __user *argp = (void __user *)arg;
>  
>  	/* Check type and command number */
> @@ -902,9 +903,15 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  			return -EFAULT;
>  		break;
>  	case PI433_IOC_WR_TX_CFG:
> -		if (copy_from_user(&instance->tx_cfg, argp,
> -				   sizeof(struct pi433_tx_cfg)))
> +		/* do not modify tx config while it is being copied to fifo */

There is no need for this comment, since it's obvious.  Also if you use
simpler names then the copy fits on one line:

		if (copy_from_user(&tx_cfg, argp, sizeof(tx_cfg)) {


> +		mutex_lock(&device->tx_fifo_lock);
> +		if (copy_from_user(&tx_cfg_buffer, argp,
> +				   sizeof(struct pi433_tx_cfg))) {

Sorry for the duplicate review, but it got sent to both my inboxes... :P

regards,
dan carpenter

Re: [PATCH v2] staging: pi433: fix race condition in pi433_ioctl

[Hugo Lefeuvre]

[-- Attachment #1: Type: text/plain, Size: 659 bytes --]

Hi Dan,

> There is no need for this comment, since it's obvious.  Also if you use
> simpler names then the copy fits on one line:
> 
> 		if (copy_from_user(&tx_cfg, argp, sizeof(tx_cfg)) {
> 
> 
> > +		mutex_lock(&device->tx_fifo_lock);
> > +		if (copy_from_user(&tx_cfg_buffer, argp,
> > +				   sizeof(struct pi433_tx_cfg))) {
> 
> Sorry for the duplicate review, but it got sent to both my inboxes... :P

Thanks for your review ! Patch updated.

Please tell me if you don't to be CC-ed anymore. :)

regards,
 Hugo

-- 
             Hugo Lefeuvre (hle)    |    www.owl.eu.com
4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]